node_modules

47 files changed, 5398 insertions, 0 deletions

diff --git a/node_modules/concordance/lib/Circular.js b/node_modules/concordance/lib/Circular.js
new file mode 100644
index 000000000..c5c020267
--- /dev/null
+++ b/node_modules/concordance/lib/Circular.js
@@ -0,0 +1,35 @@
+'use strict'
+
+class Circular {
+  constructor () {
+    this.stack = new Map()
+  }
+
+  add (descriptor) {
+    if (this.stack.has(descriptor)) throw new Error('Already in stack')
+
+    if (descriptor.isItem !== true && descriptor.isMapEntry !== true && descriptor.isProperty !== true) {
+      this.stack.set(descriptor, this.stack.size + 1)
+    }
+    return this
+  }
+
+  delete (descriptor) {
+    if (this.stack.has(descriptor)) {
+      if (this.stack.get(descriptor) !== this.stack.size) throw new Error('Not on top of stack')
+      this.stack.delete(descriptor)
+    }
+    return this
+  }
+
+  has (descriptor) {
+    return this.stack.has(descriptor)
+  }
+
+  get (descriptor) {
+    return this.stack.has(descriptor)
+      ? this.stack.get(descriptor)
+      : 0
+  }
+}
+module.exports = Circular
diff --git a/node_modules/concordance/lib/Indenter.js b/node_modules/concordance/lib/Indenter.js
new file mode 100644
index 000000000..deeca842e
--- /dev/null
+++ b/node_modules/concordance/lib/Indenter.js
@@ -0,0 +1,22 @@
+'use strict'
+
+class Indenter {
+  constructor (level, step) {
+    this.level = level
+    this.step = step
+    this.value = step.repeat(level)
+  }
+
+  increase () {
+    return new Indenter(this.level + 1, this.step)
+  }
+
+  decrease () {
+    return new Indenter(this.level - 1, this.step)
+  }
+
+  toString () {
+    return this.value
+  }
+}
+module.exports = Indenter
diff --git a/node_modules/concordance/lib/Registry.js b/node_modules/concordance/lib/Registry.js
new file mode 100644
index 000000000..f4a4b6808
--- /dev/null
+++ b/node_modules/concordance/lib/Registry.js
@@ -0,0 +1,24 @@
+'use strict'
+
+class Registry {
+  constructor () {
+    this.counter = 0
+    this.map = new WeakMap()
+  }
+
+  has (value) {
+    return this.map.has(value)
+  }
+
+  get (value) {
+    return this.map.get(value).descriptor
+  }
+
+  alloc (value) {
+    const index = ++this.counter
+    const pointer = {descriptor: null, index}
+    this.map.set(value, pointer)
+    return pointer
+  }
+}
+module.exports = Registry
diff --git a/node_modules/concordance/lib/compare.js b/node_modules/concordance/lib/compare.js
new file mode 100644
index 000000000..7e24228e6
--- /dev/null
+++ b/node_modules/concordance/lib/compare.js
@@ -0,0 +1,103 @@
+'use strict'
+
+const constants = require('./constants')
+const describe = require('./describe')
+const recursorUtils = require('./recursorUtils')
+const shouldCompareDeep = require('./shouldCompareDeep')
+const symbolProperties = require('./symbolProperties')
+const Circular = require('./Circular')
+
+const AMBIGUOUS = constants.AMBIGUOUS
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function shortcircuitPrimitive (value) {
+  if (value === null || value === undefined || value === true || value === false) return true
+
+  const type = typeof value
+  if (type === 'string' || type === 'symbol') return true
+  // Don't shortcircuit NaN values
+  if (type === 'number') return !isNaN(value)
+
+  return false
+}
+
+function compareDescriptors (lhs, rhs) {
+  const lhsCircular = new Circular()
+  const rhsCircular = new Circular()
+
+  const lhsStack = []
+  const rhsStack = []
+  let topIndex = -1
+
+  do {
+    let result
+    if (lhsCircular.has(lhs)) {
+      result = lhsCircular.get(lhs) === rhsCircular.get(rhs)
+        ? DEEP_EQUAL
+        : UNEQUAL
+    } else if (rhsCircular.has(rhs)) {
+      result = UNEQUAL
+    } else {
+      result = lhs.compare(rhs)
+    }
+
+    if (result === UNEQUAL) return false
+    if (result !== DEEP_EQUAL) {
+      if (!shouldCompareDeep(result, lhs, rhs)) return false
+
+      if (result === AMBIGUOUS && lhs.isProperty === true) {
+        // Replace both sides by a pseudo-descriptor which collects symbol
+        // properties instead.
+        lhs = new symbolProperties.Collector(lhs, lhsStack[topIndex].recursor)
+        rhs = new symbolProperties.Collector(rhs, rhsStack[topIndex].recursor)
+        // Replace the current recursors so they can continue correctly after
+        // the collectors have been "compared". This is necessary since the
+        // collectors eat the first value after the last symbol property.
+        lhsStack[topIndex].recursor = recursorUtils.unshift(lhsStack[topIndex].recursor, lhs.collectAll())
+        rhsStack[topIndex].recursor = recursorUtils.unshift(rhsStack[topIndex].recursor, rhs.collectAll())
+      }
+
+      lhsCircular.add(lhs)
+      rhsCircular.add(rhs)
+
+      lhsStack.push({ subject: lhs, recursor: lhs.createRecursor() })
+      rhsStack.push({ subject: rhs, recursor: rhs.createRecursor() })
+      topIndex++
+    }
+
+    while (topIndex >= 0) {
+      lhs = lhsStack[topIndex].recursor()
+      rhs = rhsStack[topIndex].recursor()
+      if (lhs !== null && rhs !== null) {
+        break
+      }
+
+      if (lhs === null && rhs === null) {
+        const lhsRecord = lhsStack.pop()
+        const rhsRecord = rhsStack.pop()
+        lhsCircular.delete(lhsRecord.subject)
+        rhsCircular.delete(rhsRecord.subject)
+        topIndex--
+      } else {
+        return false
+      }
+    }
+  } while (topIndex >= 0)
+
+  return true
+}
+exports.compareDescriptors = compareDescriptors
+
+function compare (actual, expected, options) {
+  if (Object.is(actual, expected)) return { pass: true }
+  // Primitive values should be the same, so if actual or expected is primitive
+  // then the values will never compare.
+  if (shortcircuitPrimitive(actual) || shortcircuitPrimitive(expected)) return { pass: false }
+
+  actual = describe(actual, options)
+  expected = describe(expected, options)
+  const pass = compareDescriptors(actual, expected)
+  return { actual, expected, pass }
+}
+exports.compare = compare
diff --git a/node_modules/concordance/lib/complexValues/arguments.js b/node_modules/concordance/lib/complexValues/arguments.js
new file mode 100644
index 000000000..446407222
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/arguments.js
@@ -0,0 +1,48 @@
+'use strict'
+
+const constants = require('../constants')
+const object = require('./object')
+
+const AMBIGUOUS = constants.AMBIGUOUS
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  return new DescribedArgumentsValue(Object.assign({
+    // Treat as an array, to allow comparisons with arrays
+    isArray: true,
+    isList: true
+  }, props, { ctor: 'Arguments' }))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedArgumentsValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('ArgumentsValue')
+exports.tag = tag
+
+class ArgumentsValue extends object.ObjectValue {
+  compare (expected) {
+    if (expected.isComplex !== true) return UNEQUAL
+
+    // When used on the left-hand side of a comparison, argument values may be
+    // compared to arrays.
+    if (expected.stringTag === 'Array') return AMBIGUOUS
+
+    return super.compare(expected)
+  }
+}
+Object.defineProperty(ArgumentsValue.prototype, 'tag', { value: tag })
+
+const DescribedArgumentsValue = object.DescribedMixin(ArgumentsValue)
+
+class DeserializedArgumentsValue extends object.DeserializedMixin(ArgumentsValue) {
+  compare (expected) {
+    // Deserialized argument values may only be compared to argument values.
+    return expected.isComplex === true && expected.stringTag === 'Array'
+      ? UNEQUAL
+      : super.compare(expected)
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/arrayBuffer.js b/node_modules/concordance/lib/complexValues/arrayBuffer.js
new file mode 100644
index 000000000..1053b893e
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/arrayBuffer.js
@@ -0,0 +1,30 @@
+'use strict'
+
+const typedArray = require('./typedArray')
+
+function describe (props) {
+  return new DescribedArrayBufferValue(Object.assign({
+    // Assume at least Node.js 4.5.0, which introduces Buffer.from()
+    buffer: Buffer.from(props.value),
+    // Set isArray and isList so the property recursor excludes the byte accessors
+    isArray: true,
+    isList: true
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedArrayBufferValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('ArrayBufferValue')
+exports.tag = tag
+
+// ArrayBuffers can be represented as regular Buffers, allowing them to be
+// treated as TypedArrays for the purposes of this package.
+class ArrayBufferValue extends typedArray.TypedArrayValue {}
+Object.defineProperty(ArrayBufferValue.prototype, 'tag', { value: tag })
+
+const DescribedArrayBufferValue = typedArray.DescribedMixin(ArrayBufferValue)
+const DeserializedArrayBufferValue = typedArray.DeserializedMixin(ArrayBufferValue)
diff --git a/node_modules/concordance/lib/complexValues/boxed.js b/node_modules/concordance/lib/complexValues/boxed.js
new file mode 100644
index 000000000..3736ad137
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/boxed.js
@@ -0,0 +1,51 @@
+'use strict'
+
+const recursorUtils = require('../recursorUtils')
+const stringPrimitive = require('../primitiveValues/string').tag
+const object = require('./object')
+
+function describe (props) {
+  return new DescribedBoxedValue(props)
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedBoxedValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('BoxedValue')
+exports.tag = tag
+
+class BoxedValue extends object.ObjectValue {}
+Object.defineProperty(BoxedValue.prototype, 'tag', {value: tag})
+
+class DescribedBoxedValue extends object.DescribedMixin(BoxedValue) {
+  constructor (props) {
+    super(props)
+    this.unboxed = props.unboxed
+  }
+
+  createListRecursor () {
+    return recursorUtils.NOOP_RECURSOR
+  }
+
+  createPropertyRecursor () {
+    if (this.unboxed.tag !== stringPrimitive) return super.createPropertyRecursor()
+
+    // Just so that createPropertyRecursor() skips the index-based character
+    // properties.
+    try {
+      this.isList = true
+      return super.createPropertyRecursor()
+    } finally {
+      this.isList = false
+    }
+  }
+
+  createRecursor () {
+    return recursorUtils.unshift(super.createRecursor(), this.unboxed)
+  }
+}
+
+const DeserializedBoxedValue = object.DeserializedMixin(BoxedValue)
diff --git a/node_modules/concordance/lib/complexValues/dataView.js b/node_modules/concordance/lib/complexValues/dataView.js
new file mode 100644
index 000000000..0dd6199f6
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/dataView.js
@@ -0,0 +1,29 @@
+'use strict'
+
+const typedArray = require('./typedArray')
+
+function describe (props) {
+  return new DescribedDataViewValue(Object.assign({
+    buffer: typedArray.getBuffer(props.value),
+    // Set isArray and isList so the property recursor excludes the byte accessors
+    isArray: true,
+    isList: true
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedDataViewValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('DataViewValue')
+exports.tag = tag
+
+// DataViews can be represented as regular Buffers, allowing them to be treated
+// as TypedArrays for the purposes of this package.
+class DataViewValue extends typedArray.TypedArrayValue {}
+Object.defineProperty(DataViewValue.prototype, 'tag', { value: tag })
+
+const DescribedDataViewValue = typedArray.DescribedMixin(DataViewValue)
+const DeserializedDataViewValue = typedArray.DeserializedMixin(DataViewValue)
diff --git a/node_modules/concordance/lib/complexValues/date.js b/node_modules/concordance/lib/complexValues/date.js
new file mode 100644
index 000000000..b437456b8
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/date.js
@@ -0,0 +1,89 @@
+'use strict'
+
+const dateTime = require('date-time')
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+const object = require('./object')
+
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  const date = props.value
+  const invalid = isNaN(date.valueOf())
+  return new DescribedDateValue(Object.assign({}, props, {invalid}))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedDateValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('DateValue')
+exports.tag = tag
+
+function formatDate (date) {
+  // Always format in UTC. The local timezone shouldn't be used since it's most
+  // likely different from that of CI servers.
+  return dateTime({
+    date,
+    local: false,
+    showTimeZone: true,
+    showMilliseconds: true
+  })
+}
+
+class DateValue extends object.ObjectValue {
+  constructor (props) {
+    super(props)
+    this.invalid = props.invalid
+  }
+
+  compare (expected) {
+    const result = super.compare(expected)
+    if (result !== SHALLOW_EQUAL) return result
+
+    return (this.invalid && expected.invalid) || Object.is(this.value.getTime(), expected.value.getTime())
+      ? SHALLOW_EQUAL
+      : UNEQUAL
+  }
+
+  formatShallow (theme, indent) {
+    const string = formatUtils.formatCtorAndStringTag(theme, this) + ' ' +
+      (this.invalid ? theme.date.invalid : formatUtils.wrap(theme.date.value, formatDate(this.value))) + ' ' +
+      theme.object.openBracket
+
+    return super.formatShallow(theme, indent).customize({
+      finalize (innerLines) {
+        return innerLines.isEmpty
+          ? lineBuilder.single(string + theme.object.closeBracket)
+          : lineBuilder.first(string)
+              .concat(innerLines.withFirstPrefixed(indent.increase()).stripFlags())
+              .append(lineBuilder.last(indent + theme.object.closeBracket))
+      },
+
+      maxDepth () {
+        return lineBuilder.single(string + ' ' + theme.maxDepth + ' ' + theme.object.closeBracket)
+      }
+    })
+  }
+
+  serialize () {
+    const iso = this.invalid ? null : this.value.toISOString()
+    return [this.invalid, iso, super.serialize()]
+  }
+}
+Object.defineProperty(DateValue.prototype, 'tag', { value: tag })
+
+const DescribedDateValue = object.DescribedMixin(DateValue)
+
+class DeserializedDateValue extends object.DeserializedMixin(DateValue) {
+  constructor (state, recursor) {
+    super(state[2], recursor)
+    this.invalid = state[0]
+    this.value = new Date(this.invalid ? NaN : state[1])
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/error.js b/node_modules/concordance/lib/complexValues/error.js
new file mode 100644
index 000000000..781dd7e87
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/error.js
@@ -0,0 +1,133 @@
+'use strict'
+
+const constants = require('../constants')
+const isEnumerable = require('../isEnumerable')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+const NOOP_RECURSOR = require('../recursorUtils').NOOP_RECURSOR
+const object = require('./object')
+
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  const error = props.value
+  return new DescribedErrorValue(Object.assign({
+    nameIsEnumerable: isEnumerable(error, 'name'),
+    name: error.name,
+    messageIsEnumerable: isEnumerable(error, 'message'),
+    message: error.message
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedErrorValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('ErrorValue')
+exports.tag = tag
+
+class ErrorValue extends object.ObjectValue {
+  constructor (props) {
+    super(props)
+    this.name = props.name
+  }
+
+  compare (expected) {
+    return this.tag === expected.tag && this.name === expected.name
+      ? super.compare(expected)
+      : UNEQUAL
+  }
+
+  formatShallow (theme, indent) {
+    const name = this.name || this.ctor
+
+    let string = name
+      ? formatUtils.wrap(theme.error.name, name)
+      : formatUtils.wrap(theme.object.stringTag, this.stringTag)
+    if (this.ctor && this.ctor !== name) {
+      string += ' ' + formatUtils.wrap(theme.error.ctor, this.ctor)
+    }
+    if (this.stringTag && this.stringTag !== this.ctor && this.name && !this.name.includes(this.stringTag)) {
+      string += ' ' + formatUtils.wrap(theme.object.secondaryStringTag, this.stringTag)
+    }
+    string += ' ' + theme.object.openBracket
+
+    return super.formatShallow(theme, indent).customize({
+      finalize (innerLines) {
+        return innerLines.isEmpty
+          ? lineBuilder.single(string + theme.object.closeBracket)
+          : lineBuilder.first(string)
+              .concat(innerLines.withFirstPrefixed(indent.increase()).stripFlags())
+              .append(lineBuilder.last(indent + theme.object.closeBracket))
+      },
+
+      maxDepth () {
+        return lineBuilder.single(string + ' ' + theme.maxDepth + ' ' + theme.object.closeBracket)
+      }
+    })
+  }
+
+  serialize () {
+    return [this.name, super.serialize()]
+  }
+}
+Object.defineProperty(ErrorValue.prototype, 'tag', { value: tag })
+
+class DescribedErrorValue extends object.DescribedMixin(ErrorValue) {
+  constructor (props) {
+    super(props)
+    this.nameIsEnumerable = props.nameIsEnumerable
+    this.messageIsEnumerable = props.messageIsEnumerable
+    this.message = props.message
+  }
+
+  createPropertyRecursor () {
+    const recursor = super.createPropertyRecursor()
+
+    let skipName = this.nameIsEnumerable
+    let emitMessage = !this.messageIsEnumerable
+
+    let size = recursor.size
+    if (skipName && size > 0) {
+      size -= 1
+    }
+    if (emitMessage) {
+      size += 1
+    }
+
+    if (size === 0) return NOOP_RECURSOR
+
+    let done = false
+    const next = () => {
+      if (done) return null
+
+      const property = recursor.next()
+      if (property) {
+        if (skipName && property.key.value === 'name') {
+          skipName = false
+          return next()
+        }
+        return property
+      }
+
+      if (emitMessage) {
+        emitMessage = false
+        return this.describeProperty('message', this.describeAny(this.message))
+      }
+
+      done = true
+      return null
+    }
+
+    return { size, next }
+  }
+}
+
+class DeserializedErrorValue extends object.DeserializedMixin(ErrorValue) {
+  constructor (state, recursor) {
+    super(state[1], recursor)
+    this.name = state[0]
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/function.js b/node_modules/concordance/lib/complexValues/function.js
new file mode 100644
index 000000000..4ddd38f39
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/function.js
@@ -0,0 +1,159 @@
+'use strict'
+
+const functionNameSupport = require('function-name-support')
+
+const constants = require('../constants')
+const getStringTag = require('../getStringTag')
+const isEnumerable = require('../isEnumerable')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+const NOOP_RECURSOR = require('../recursorUtils').NOOP_RECURSOR
+const object = require('./object')
+
+const UNEQUAL = constants.UNEQUAL
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+
+// Node.js 4 provides Function, more recent versions use GeneratorFunction
+const generatorsHaveGeneratorTag = getStringTag(function * () {}) === 'GeneratorFunction'
+
+function describe (props) {
+  const fn = props.value
+  return new DescribedFunctionValue(Object.assign({
+    nameIsEnumerable: isEnumerable(fn, 'name'),
+    name: typeof fn.name === 'string' ? fn.name : null
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedFunctionValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('FunctionValue')
+exports.tag = tag
+
+class FunctionValue extends object.ObjectValue {
+  constructor (props) {
+    super(props)
+    this.name = props.name
+  }
+
+  formatShallow (theme, indent) {
+    const string = formatUtils.wrap(theme.function.stringTag, this.stringTag) +
+      (this.name ? ' ' + formatUtils.wrap(theme.function.name, this.name) : '') +
+      ' ' + theme.object.openBracket
+
+    return super.formatShallow(theme, indent).customize({
+      finalize (innerLines) {
+        return innerLines.isEmpty
+          ? lineBuilder.single(string + theme.object.closeBracket)
+          : lineBuilder.first(string)
+              .concat(innerLines.withFirstPrefixed(indent.increase()).stripFlags())
+              .append(lineBuilder.last(indent + theme.object.closeBracket))
+      },
+
+      maxDepth () {
+        return lineBuilder.single(string + ' ' + theme.maxDepth + ' ' + theme.object.closeBracket)
+      }
+    })
+  }
+}
+Object.defineProperty(FunctionValue.prototype, 'tag', { value: tag })
+
+class DescribedFunctionValue extends object.DescribedMixin(FunctionValue) {
+  constructor (props) {
+    super(props)
+    this.nameIsEnumerable = props.nameIsEnumerable
+  }
+
+  compare (expected) {
+    if (this.tag !== expected.tag) return UNEQUAL
+    if (this.name !== expected.name) return UNEQUAL
+    if (this.value && expected.value && this.value !== expected.value) return UNEQUAL
+
+    return super.compare(expected)
+  }
+
+  createPropertyRecursor () {
+    const recursor = super.createPropertyRecursor()
+
+    const skipName = this.nameIsEnumerable
+    if (!skipName) return recursor
+
+    let size = recursor.size
+    if (skipName) {
+      size -= 1
+    }
+
+    if (size === 0) return NOOP_RECURSOR
+
+    const next = () => {
+      const property = recursor.next()
+      if (property) {
+        if (skipName && property.key.value === 'name') {
+          return next()
+        }
+        return property
+      }
+
+      return null
+    }
+
+    return { size, next }
+  }
+
+  serialize () {
+    return [this.name, generatorsHaveGeneratorTag, super.serialize()]
+  }
+}
+
+class DeserializedFunctionValue extends object.DeserializedMixin(FunctionValue) {
+  constructor (state, recursor) {
+    super(state[2], recursor)
+    this.name = state[0]
+    this.trustStringTag = state[1]
+  }
+
+  compare (expected) {
+    if (this.tag !== expected.tag) return UNEQUAL
+
+    if (this.name !== expected.name) {
+      if (this.functionNameSupportFlags === functionNameSupport.bitFlags) {
+        // The engine used to create the serialization supports the same
+        // function name inference as the current engine. That said, unless
+        // the engine has full support for name inference, it's possible that
+        // names were lost simply due to refactoring. Names are unequal if
+        // the engine has full support, or if names were inferred.
+        if (functionNameSupport.hasFullSupport === true || (this.name !== '' && expected.name !== '')) return UNEQUAL
+      } else if (functionNameSupport.isSubsetOf(this.functionNameSupportFlags)) {
+        // The engine used to create the serialization could infer more function
+        // names than the current engine. Assume `expected.name` comes from the
+        // current engine and treat the names as unequal only if the current
+        // engine could infer a name.
+        if (expected.name !== '') return UNEQUAL
+      } else {
+        /* istanbul ignore else */
+        if (functionNameSupport.isSupersetOf(this.functionNameSupportFlags)) {
+          // The engine used to create the serialization could infer fewer
+          // function names than the current engine. Treat the names as unequal
+          // only if a name was in the serialization.
+          if (this.name !== '') return UNEQUAL
+        }
+      }
+    }
+
+    // Assume `stringTag` is either 'Function' or 'GeneratorFunction', and that
+    // it always equals `ctor`. Since Node.js 4 only provides 'Function', even
+    // for generator functions, only compare `stringTag` if the serialized value
+    // legitimately would have been `Function`, and the expected `stringTag` can
+    // reliably be inferred.
+    if (this.trustStringTag && generatorsHaveGeneratorTag && this.stringTag !== expected.stringTag) return UNEQUAL
+
+    return SHALLOW_EQUAL
+  }
+
+  serialize () {
+    return [this.name, this.trustStringTag, super.serialize()]
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/global.js b/node_modules/concordance/lib/complexValues/global.js
new file mode 100644
index 000000000..6acd66d7a
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/global.js
@@ -0,0 +1,33 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe () {
+  return new GlobalValue()
+}
+exports.describe = describe
+
+exports.deserialize = describe
+
+const tag = Symbol('GlobalValue')
+exports.tag = tag
+
+class GlobalValue {
+  compare (expected) {
+    return this.tag === expected.tag
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatDeep (theme) {
+    return lineBuilder.single(
+      formatUtils.wrap(theme.global, 'Global') + ' ' + theme.object.openBracket + theme.object.closeBracket)
+  }
+}
+Object.defineProperty(GlobalValue.prototype, 'isComplex', { value: true })
+Object.defineProperty(GlobalValue.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/complexValues/map.js b/node_modules/concordance/lib/complexValues/map.js
new file mode 100644
index 000000000..7ff13b217
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/map.js
@@ -0,0 +1,78 @@
+'use strict'
+
+const constants = require('../constants')
+const recursorUtils = require('../recursorUtils')
+const object = require('./object')
+
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  return new DescribedMapValue(Object.assign({
+    size: props.value.size
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedMapValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('MapValue')
+exports.tag = tag
+
+class MapValue extends object.ObjectValue {
+  constructor (props) {
+    super(props)
+    this.size = props.size
+  }
+
+  compare (expected) {
+    const result = super.compare(expected)
+    if (result !== SHALLOW_EQUAL) return result
+
+    return this.size === expected.size
+      ? SHALLOW_EQUAL
+      : UNEQUAL
+  }
+
+  prepareDiff (expected) {
+    // Maps should be compared, even if they have a different number of entries.
+    return {compareResult: super.compare(expected)}
+  }
+
+  serialize () {
+    return [this.size, super.serialize()]
+  }
+}
+Object.defineProperty(MapValue.prototype, 'tag', { value: tag })
+
+class DescribedMapValue extends object.DescribedMixin(MapValue) {
+  createIterableRecursor () {
+    const size = this.size
+    if (size === 0) return recursorUtils.NOOP_RECURSOR
+
+    let index = 0
+    let entries
+    const next = () => {
+      if (index === size) return null
+
+      if (!entries) {
+        entries = Array.from(this.value)
+      }
+
+      const entry = entries[index++]
+      return this.describeMapEntry(this.describeAny(entry[0]), this.describeAny(entry[1]))
+    }
+
+    return { size, next }
+  }
+}
+
+class DeserializedMapValue extends object.DeserializedMixin(MapValue) {
+  constructor (state, recursor) {
+    super(state[1], recursor)
+    this.size = state[0]
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/object.js b/node_modules/concordance/lib/complexValues/object.js
new file mode 100644
index 000000000..97a59285c
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/object.js
@@ -0,0 +1,283 @@
+'use strict'
+
+const functionNameSupport = require('function-name-support')
+
+const constants = require('../constants')
+const getObjectKeys = require('../getObjectKeys')
+const ObjectFormatter = require('../formatUtils').ObjectFormatter
+const hasLength = require('../hasLength')
+const recursorUtils = require('../recursorUtils')
+const stats = require('../metaDescriptors/stats')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  const isArray = props.stringTag === 'Array'
+  const object = props.value
+  return new DescribedObjectValue(Object.assign({
+    isArray,
+    isIterable: object[Symbol.iterator] !== undefined,
+    isList: isArray || hasLength(object)
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedObjectValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('ObjectValue')
+exports.tag = tag
+
+class ObjectValue {
+  constructor (props) {
+    this.ctor = props.ctor
+    this.pointer = props.pointer
+    this.stringTag = props.stringTag
+
+    this.isArray = props.isArray === true
+    this.isIterable = props.isIterable === true
+    this.isList = props.isList === true
+  }
+
+  compare (expected) {
+    if (this.tag !== expected.tag) return UNEQUAL
+    if (this.stringTag !== expected.stringTag || !this.hasSameCtor(expected)) return UNEQUAL
+    return SHALLOW_EQUAL
+  }
+
+  hasSameCtor (expected) {
+    return this.ctor === expected.ctor
+  }
+
+  formatShallow (theme, indent) {
+    return new ObjectFormatter(this, theme, indent)
+  }
+
+  serialize () {
+    return [
+      this.ctor, this.pointer, this.stringTag,
+      this.isArray, this.isIterable, this.isList,
+      functionNameSupport.bitFlags
+    ]
+  }
+}
+Object.defineProperty(ObjectValue.prototype, 'isComplex', { value: true })
+Object.defineProperty(ObjectValue.prototype, 'tag', { value: tag })
+exports.ObjectValue = ObjectValue
+
+const DescribedObjectValue = DescribedMixin(ObjectValue)
+const DeserializedObjectValue = DeserializedMixin(ObjectValue)
+
+function DescribedMixin (base) {
+  return class extends base {
+    constructor (props) {
+      super(props)
+
+      this.value = props.value
+      this.describeAny = props.describeAny
+      this.describeItem = props.describeItem
+      this.describeMapEntry = props.describeMapEntry
+      this.describeProperty = props.describeProperty
+
+      this.iterableState = null
+      this.listState = null
+      this.propertyState = null
+    }
+
+    compare (expected) {
+      return this.value === expected.value
+        ? DEEP_EQUAL
+        : super.compare(expected)
+    }
+
+    createPropertyRecursor () {
+      const objectKeys = getObjectKeys(this.value, this.isList ? this.value.length : 0)
+      const size = objectKeys.size
+      if (size === 0) return recursorUtils.NOOP_RECURSOR
+
+      let index = 0
+      const next = () => {
+        if (index === size) return null
+
+        const key = objectKeys.keys[index++]
+        return this.describeProperty(key, this.describeAny(this.value[key]))
+      }
+
+      return { size, next }
+    }
+
+    createListRecursor () {
+      if (!this.isList) return recursorUtils.NOOP_RECURSOR
+
+      const size = this.value.length
+      if (size === 0) return recursorUtils.NOOP_RECURSOR
+
+      let index = 0
+      const next = () => {
+        if (index === size) return null
+
+        const current = index
+        index++
+        return this.describeItem(current, this.describeAny(this.value[current]))
+      }
+
+      return { size, next }
+    }
+
+    createIterableRecursor () {
+      if (this.isArray || !this.isIterable) return recursorUtils.NOOP_RECURSOR
+
+      const iterator = this.value[Symbol.iterator]()
+      let first = iterator.next()
+
+      let done = false
+      let size = -1
+      if (first.done) {
+        if (first.value === undefined) {
+          size = 0
+          done = true
+        } else {
+          size = 1
+        }
+      }
+
+      let index = 0
+      const next = () => {
+        if (done) return null
+
+        while (!done) {
+          const current = first || iterator.next()
+          if (current === first) {
+            first = null
+          }
+          if (current.done) {
+            done = true
+          }
+
+          const item = current.value
+          if (done && item === undefined) return null
+
+          if (this.isList && this.value[index] === item) {
+            index++
+          } else {
+            return this.describeItem(index++, this.describeAny(item))
+          }
+        }
+      }
+
+      return { size, next }
+    }
+
+    createRecursor () {
+      let recursedProperty = false
+      let recursedList = false
+      let recursedIterable = false
+
+      let recursor = null
+      return () => {
+        let retval = null
+        do {
+          if (recursor !== null) {
+            retval = recursor.next()
+            if (retval === null) {
+              recursor = null
+            }
+          }
+
+          while (recursor === null && (!recursedList || !recursedProperty || !recursedIterable)) {
+            // Prioritize recursing lists
+            if (!recursedList) {
+              const replay = recursorUtils.replay(this.listState, () => this.createListRecursor())
+              this.listState = replay.state
+              recursor = replay.recursor
+              recursedList = true
+              if (recursor !== recursorUtils.NOOP_RECURSOR) {
+                retval = stats.describeListRecursor(recursor)
+              }
+            } else if (!recursedProperty) {
+              const replay = recursorUtils.replay(this.propertyState, () => this.createPropertyRecursor())
+              this.propertyState = replay.state
+              recursor = replay.recursor
+              recursedProperty = true
+              if (recursor !== recursorUtils.NOOP_RECURSOR) {
+                retval = stats.describePropertyRecursor(recursor)
+              }
+            } else if (!recursedIterable) {
+              const replay = recursorUtils.replay(this.iterableState, () => this.createIterableRecursor())
+              this.iterableState = replay.state
+              recursor = replay.recursor
+              recursedIterable = true
+              if (recursor !== recursorUtils.NOOP_RECURSOR) {
+                retval = stats.describeIterableRecursor(recursor)
+              }
+            }
+          }
+        } while (recursor !== null && retval === null)
+
+        return retval
+      }
+    }
+  }
+}
+exports.DescribedMixin = DescribedMixin
+
+function DeserializedMixin (base) {
+  return class extends base {
+    constructor (state, recursor) {
+      super({
+        ctor: state[0],
+        pointer: state[1],
+        stringTag: state[2],
+        isArray: state[3],
+        isIterable: state[4],
+        isList: state[5]
+      })
+
+      this.functionNameSupportFlags = state[6]
+      this.deserializedRecursor = recursor
+      this.replayState = null
+    }
+
+    createRecursor () {
+      if (!this.deserializedRecursor) return () => null
+
+      const replay = recursorUtils.replay(this.replayState, () => ({ size: -1, next: this.deserializedRecursor }))
+      this.replayState = replay.state
+      return replay.recursor.next
+    }
+
+    hasSameCtor (expected) {
+      if (this.ctor === expected.ctor) return true
+
+      if (this.functionNameSupportFlags === functionNameSupport.bitFlags) {
+        // The engine used to create the serialization supports the same
+        // function name inference as the current engine. That said, unless
+        // the engine has full support for name inference, it's possible that
+        // names were lost simply due to refactoring. Ctors are not the same
+        // only if the engine has full support, or if ctors were inferred.
+        if (functionNameSupport.hasFullSupport === true || (this.ctor !== null && expected.ctor !== null)) return false
+      } else if (functionNameSupport.isSubsetOf(this.functionNameSupportFlags)) {
+        // The engine used to create the serialization could infer more function
+        // names than the current engine. Assume `expected.ctor` comes from the
+        // current engine and treat the ctors as unequal only if the current
+        // engine could infer a ctor.
+        if (expected.ctor !== null) return false
+      } else {
+        /* istanbul ignore else */
+        if (functionNameSupport.isSupersetOf(this.functionNameSupportFlags)) {
+          // The engine used to create the serialization could infer fewer
+          // function names than the current engine. Treat the ctors as unequal
+          // only if a ctor was in the serialization.
+          if (this.ctor !== null) return false
+        }
+      }
+
+      return true
+    }
+  }
+}
+exports.DeserializedMixin = DeserializedMixin
diff --git a/node_modules/concordance/lib/complexValues/promise.js b/node_modules/concordance/lib/complexValues/promise.js
new file mode 100644
index 000000000..823d45386
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/promise.js
@@ -0,0 +1,40 @@
+'use strict'
+
+const constants = require('../constants')
+const object = require('./object')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  return new DescribedPromiseValue(props)
+}
+exports.describe = describe
+
+function deserialize (props) {
+  return new DeserializedPromiseValue(props)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('PromiseValue')
+exports.tag = tag
+
+class PromiseValue extends object.ObjectValue {}
+Object.defineProperty(PromiseValue.prototype, 'tag', { value: tag })
+
+class DescribedPromiseValue extends object.DescribedMixin(PromiseValue) {
+  compare (expected) {
+    // When comparing described promises, require them to be the exact same
+    // object.
+    return super.compare(expected) === DEEP_EQUAL
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+}
+
+class DeserializedPromiseValue extends object.DeserializedMixin(PromiseValue) {
+  compare (expected) {
+    // Deserialized promises can never be compared using object references.
+    return super.compare(expected)
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/regexp.js b/node_modules/concordance/lib/complexValues/regexp.js
new file mode 100644
index 000000000..1c66a2fd8
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/regexp.js
@@ -0,0 +1,90 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+const object = require('./object')
+
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  const regexp = props.value
+  return new DescribedRegexpValue(Object.assign({
+    flags: getSortedFlags(regexp),
+    source: regexp.source
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedRegexpValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('RegexpValue')
+exports.tag = tag
+
+function getSortedFlags (regexp) {
+  const flags = regexp.flags || String(regexp).slice(regexp.source.length + 2)
+  return flags.split('').sort().join('')
+}
+
+class RegexpValue extends object.ObjectValue {
+  constructor (props) {
+    super(props)
+    this.flags = props.flags
+    this.source = props.source
+  }
+
+  compare (expected) {
+    return this.tag === expected.tag && this.flags === expected.flags && this.source === expected.source
+      ? super.compare(expected)
+      : UNEQUAL
+  }
+
+  formatShallow (theme, indent) {
+    const ctor = this.ctor || this.stringTag
+    const regexp = formatUtils.wrap(theme.regexp.source, this.source) + formatUtils.wrap(theme.regexp.flags, this.flags)
+
+    return super.formatShallow(theme, indent).customize({
+      finalize: innerLines => {
+        if (ctor === 'RegExp' && innerLines.isEmpty) return lineBuilder.single(regexp)
+
+        const innerIndentation = indent.increase()
+        const header = lineBuilder.first(formatUtils.formatCtorAndStringTag(theme, this) + ' ' + theme.object.openBracket)
+          .concat(lineBuilder.line(innerIndentation + regexp))
+
+        if (!innerLines.isEmpty) {
+          header.append(lineBuilder.line(innerIndentation + theme.regexp.separator))
+          header.append(innerLines.withFirstPrefixed(innerIndentation).stripFlags())
+        }
+
+        return header.append(lineBuilder.last(indent + theme.object.closeBracket))
+      },
+
+      maxDepth: () => {
+        return lineBuilder.single(
+          formatUtils.formatCtorAndStringTag(theme, this) + ' ' +
+          theme.object.openBracket + ' ' +
+          regexp + ' ' +
+          theme.maxDepth + ' ' +
+          theme.object.closeBracket)
+      }
+    })
+  }
+
+  serialize () {
+    return [this.flags, this.source, super.serialize()]
+  }
+}
+Object.defineProperty(RegexpValue.prototype, 'tag', { value: tag })
+
+const DescribedRegexpValue = object.DescribedMixin(RegexpValue)
+
+class DeserializedRegexpValue extends object.DeserializedMixin(RegexpValue) {
+  constructor (state, recursor) {
+    super(state[2], recursor)
+    this.flags = state[0]
+    this.source = state[1]
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/set.js b/node_modules/concordance/lib/complexValues/set.js
new file mode 100644
index 000000000..fc3623ace
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/set.js
@@ -0,0 +1,78 @@
+'use strict'
+
+const constants = require('../constants')
+const recursorUtils = require('../recursorUtils')
+const object = require('./object')
+
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (props) {
+  return new DescribedSetValue(Object.assign({
+    size: props.value.size
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedSetValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('SetValue')
+exports.tag = tag
+
+class SetValue extends object.ObjectValue {
+  constructor (props) {
+    super(props)
+    this.size = props.size
+  }
+
+  compare (expected) {
+    const result = super.compare(expected)
+    if (result !== SHALLOW_EQUAL) return result
+
+    return this.size === expected.size
+      ? SHALLOW_EQUAL
+      : UNEQUAL
+  }
+
+  prepareDiff (expected) {
+    // Sets should be compared, even if they have a different number of items.
+    return {compareResult: super.compare(expected)}
+  }
+
+  serialize () {
+    return [this.size, super.serialize()]
+  }
+}
+Object.defineProperty(SetValue.prototype, 'tag', { value: tag })
+
+class DescribedSetValue extends object.DescribedMixin(SetValue) {
+  createIterableRecursor () {
+    const size = this.size
+    if (size === 0) return recursorUtils.NOOP_RECURSOR
+
+    let index = 0
+    let members
+    const next = () => {
+      if (index === size) return null
+
+      if (!members) {
+        members = Array.from(this.value)
+      }
+
+      const value = members[index]
+      return this.describeItem(index++, this.describeAny(value))
+    }
+
+    return { size, next }
+  }
+}
+
+class DeserializedSetValue extends object.DeserializedMixin(SetValue) {
+  constructor (state, recursor) {
+    super(state[1], recursor)
+    this.size = state[0]
+  }
+}
diff --git a/node_modules/concordance/lib/complexValues/typedArray.js b/node_modules/concordance/lib/complexValues/typedArray.js
new file mode 100644
index 000000000..5c482ff1f
--- /dev/null
+++ b/node_modules/concordance/lib/complexValues/typedArray.js
@@ -0,0 +1,162 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+const recursorUtils = require('../recursorUtils')
+const propertyStatsTag = require('../metaDescriptors/stats').propertyTag
+const object = require('./object')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function getBuffer (value) {
+  // Assume at least Node.js 4.5.0, which introduces Buffer.from()
+  const buffer = Buffer.from(value.buffer)
+  return value.byteLength !== value.buffer.byteLength
+    ? buffer.slice(value.byteOffset, value.byteOffset + value.byteLength)
+    : buffer
+}
+exports.getBuffer = getBuffer
+
+function describe (props) {
+  return new DescribedTypedArrayValue(Object.assign({
+    buffer: getBuffer(props.value),
+    // Set isArray and isList so the property recursor excludes the byte accessors
+    isArray: true,
+    isList: true
+  }, props))
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  return new DeserializedTypedArrayValue(state, recursor)
+}
+exports.deserialize = deserialize
+
+function deserializeBytes (buffer) {
+  return new Bytes(buffer)
+}
+exports.deserializeBytes = deserializeBytes
+
+const bytesTag = Symbol('Bytes')
+exports.bytesTag = bytesTag
+
+const tag = Symbol('TypedArrayValue')
+exports.tag = tag
+
+class Bytes {
+  constructor (buffer) {
+    this.buffer = buffer
+  }
+
+  compare (expected) {
+    return expected.tag === bytesTag && this.buffer.equals(expected.buffer)
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatDeep (theme, indent) {
+    const indentation = indent
+    const lines = lineBuilder.buffer()
+
+    // Display 4-byte words, 8 per line
+    let string = ''
+    let isFirst = true
+    for (let offset = 0; offset < this.buffer.length; offset += 4) {
+      if (offset > 0) {
+        if (offset % 32 === 0) {
+          if (isFirst) {
+            lines.append(lineBuilder.first(string))
+            isFirst = false
+          } else {
+            lines.append(lineBuilder.line(string))
+          }
+          string = String(indentation)
+        } else {
+          string += ' '
+        }
+      }
+      string += formatUtils.wrap(theme.typedArray.bytes, this.buffer.toString('hex', offset, offset + 4))
+    }
+
+    return isFirst
+      ? lineBuilder.single(string)
+      : lines.append(lineBuilder.last(string))
+  }
+
+  serialize () {
+    return this.buffer
+  }
+}
+Object.defineProperty(Bytes.prototype, 'tag', { value: bytesTag })
+
+class TypedArrayValue extends object.ObjectValue {
+  constructor (props) {
+    super(props)
+    this.buffer = props.buffer
+  }
+
+  formatShallow (theme, indent) {
+    return super.formatShallow(theme, indent).customize({
+      shouldFormat (subject) {
+        if (subject.tag === propertyStatsTag) return subject.size > 1
+        if (subject.isProperty === true) return subject.key.value !== 'byteLength'
+        if (subject.tag === bytesTag) return subject.buffer.byteLength > 0
+        return true
+      }
+    })
+  }
+}
+Object.defineProperty(TypedArrayValue.prototype, 'tag', { value: tag })
+exports.TypedArrayValue = TypedArrayValue
+
+function DescribedMixin (base) {
+  return class extends object.DescribedMixin(base) {
+    // The list isn't recursed. Instead a Bytes instance is returned by the main
+    // recursor.
+    createListRecursor () {
+      return recursorUtils.NOOP_RECURSOR
+    }
+
+    createPropertyRecursor () {
+      const recursor = super.createPropertyRecursor()
+      const size = recursor.size + 1
+
+      let done = false
+      const next = () => {
+        if (done) return null
+
+        const property = recursor.next()
+        if (property) return property
+
+        done = true
+        return this.describeProperty('byteLength', this.describeAny(this.buffer.byteLength))
+      }
+
+      return { size, next }
+    }
+
+    createRecursor () {
+      return recursorUtils.unshift(super.createRecursor(), new Bytes(this.buffer))
+    }
+  }
+}
+exports.DescribedMixin = DescribedMixin
+
+const DescribedTypedArrayValue = DescribedMixin(TypedArrayValue)
+
+function DeserializedMixin (base) {
+  return class extends object.DeserializedMixin(base) {
+    constructor (state, recursor) {
+      super(state, recursor)
+
+      // Get the Bytes descriptor from the recursor. It contains the buffer.
+      const bytesDescriptor = this.createRecursor()()
+      this.buffer = bytesDescriptor.buffer
+    }
+  }
+}
+exports.DeserializedMixin = DeserializedMixin
+
+const DeserializedTypedArrayValue = DeserializedMixin(TypedArrayValue)
diff --git a/node_modules/concordance/lib/constants.js b/node_modules/concordance/lib/constants.js
new file mode 100644
index 000000000..f85235faa
--- /dev/null
+++ b/node_modules/concordance/lib/constants.js
@@ -0,0 +1,13 @@
+'use strict'
+
+const AMBIGUOUS = Symbol('AMBIGUOUS')
+const DEEP_EQUAL = Symbol('DEEP_EQUAL')
+const SHALLOW_EQUAL = Symbol('SHALLOW_EQUAL')
+const UNEQUAL = Symbol('UNEQUAL')
+
+module.exports = {
+  AMBIGUOUS,
+  DEEP_EQUAL,
+  SHALLOW_EQUAL,
+  UNEQUAL
+}
diff --git a/node_modules/concordance/lib/describe.js b/node_modules/concordance/lib/describe.js
new file mode 100644
index 000000000..a8aa94572
--- /dev/null
+++ b/node_modules/concordance/lib/describe.js
@@ -0,0 +1,170 @@
+'use strict'
+
+const argumentsValue = require('./complexValues/arguments')
+const arrayBufferValue = require('./complexValues/arrayBuffer')
+const boxedValue = require('./complexValues/boxed')
+const dataViewValue = require('./complexValues/dataView')
+const dateValue = require('./complexValues/date')
+const errorValue = require('./complexValues/error')
+const functionValue = require('./complexValues/function')
+const globalValue = require('./complexValues/global')
+const mapValue = require('./complexValues/map')
+const objectValue = require('./complexValues/object')
+const promiseValue = require('./complexValues/promise')
+const regexpValue = require('./complexValues/regexp')
+const setValue = require('./complexValues/set')
+const typedArrayValue = require('./complexValues/typedArray')
+
+const itemDescriptor = require('./metaDescriptors/item')
+const mapEntryDescriptor = require('./metaDescriptors/mapEntry')
+const propertyDescriptor = require('./metaDescriptors/property')
+
+const booleanValue = require('./primitiveValues/boolean')
+const nullValue = require('./primitiveValues/null')
+const numberValue = require('./primitiveValues/number')
+const stringValue = require('./primitiveValues/string')
+const symbolValue = require('./primitiveValues/symbol')
+const undefinedValue = require('./primitiveValues/undefined')
+
+const getCtor = require('./getCtor')
+const getStringTag = require('./getStringTag')
+const pluginRegistry = require('./pluginRegistry')
+const Registry = require('./Registry')
+
+const SpecializedComplexes = new Map([
+  ['Arguments', argumentsValue.describe],
+  ['ArrayBuffer', arrayBufferValue.describe],
+  ['DataView', dataViewValue.describe],
+  ['Date', dateValue.describe],
+  ['Error', errorValue.describe],
+  ['Float32Array', typedArrayValue.describe],
+  ['Float64Array', typedArrayValue.describe],
+  ['Function', functionValue.describe],
+  ['GeneratorFunction', functionValue.describe],
+  ['global', globalValue.describe],
+  ['Int16Array', typedArrayValue.describe],
+  ['Int32Array', typedArrayValue.describe],
+  ['Int8Array', typedArrayValue.describe],
+  ['Map', mapValue.describe],
+  ['Promise', promiseValue.describe],
+  ['RegExp', regexpValue.describe],
+  ['Set', setValue.describe],
+  ['Uint16Array', typedArrayValue.describe],
+  ['Uint32Array', typedArrayValue.describe],
+  ['Uint8Array', typedArrayValue.describe],
+  ['Uint8ClampedArray', typedArrayValue.describe]
+])
+
+function describePrimitive (value) {
+  if (value === null) return nullValue.describe()
+  if (value === undefined) return undefinedValue.describe()
+  if (value === true || value === false) return booleanValue.describe(value)
+
+  const type = typeof value
+  if (type === 'number') return numberValue.describe(value)
+  if (type === 'string') return stringValue.describe(value)
+  if (type === 'symbol') return symbolValue.describe(value)
+
+  return null
+}
+
+function unboxComplex (tag, complex) {
+  // Try to unbox by calling `valueOf()`. `describePrimitive()` will return
+  // `null` if the resulting value is not a primitive, in which case it's
+  // ignored.
+  if (typeof complex.valueOf === 'function') {
+    const value = complex.valueOf()
+    if (value !== complex) return describePrimitive(value)
+  }
+
+  return null
+}
+
+function registerPlugins (plugins) {
+  if (!Array.isArray(plugins) || plugins.length === 0) return () => null
+
+  const tryFns = pluginRegistry.getTryDescribeValues(plugins)
+  return (value, stringTag, ctor) => {
+    for (const tryDescribeValue of tryFns) {
+      const describeValue = tryDescribeValue(value, stringTag, ctor)
+      if (describeValue) return describeValue
+    }
+
+    return null
+  }
+}
+
+function describeComplex (value, registry, tryPlugins, describeAny, describeItem, describeMapEntry, describeProperty) {
+  if (registry.has(value)) return registry.get(value)
+
+  const stringTag = getStringTag(value)
+  const ctor = getCtor(stringTag, value)
+  const pointer = registry.alloc(value)
+
+  let unboxed
+  let describeValue = tryPlugins(value, stringTag, ctor)
+  if (describeValue === null) {
+    if (SpecializedComplexes.has(stringTag)) {
+      describeValue = SpecializedComplexes.get(stringTag)
+    } else {
+      unboxed = unboxComplex(stringTag, value)
+      if (unboxed !== null) {
+        describeValue = boxedValue.describe
+      } else {
+        describeValue = objectValue.describe
+      }
+    }
+  }
+
+  const descriptor = describeValue({
+    ctor,
+    describeAny,
+    describeItem,
+    describeMapEntry,
+    describeProperty,
+    pointer: pointer.index,
+    stringTag,
+    unboxed,
+    value
+  })
+  pointer.descriptor = descriptor
+  return descriptor
+}
+
+function describe (value, options) {
+  const primitive = describePrimitive(value)
+  if (primitive !== null) return primitive
+
+  const registry = new Registry()
+  const tryPlugins = registerPlugins(options && options.plugins)
+  const curriedComplex = c => {
+    return describeComplex(c, registry, tryPlugins, describeAny, describeItem, describeMapEntry, describeProperty)
+  }
+
+  const describeAny = any => {
+    const descriptor = describePrimitive(any)
+    return descriptor !== null
+      ? descriptor
+      : curriedComplex(any)
+  }
+
+  const describeItem = (index, valueDescriptor) => {
+    return valueDescriptor.isPrimitive === true
+      ? itemDescriptor.describePrimitive(index, valueDescriptor)
+      : itemDescriptor.describeComplex(index, valueDescriptor)
+  }
+
+  const describeMapEntry = (keyDescriptor, valueDescriptor) => {
+    return mapEntryDescriptor.describe(keyDescriptor, valueDescriptor)
+  }
+
+  const describeProperty = (key, valueDescriptor) => {
+    const keyDescriptor = describePrimitive(key)
+    return valueDescriptor.isPrimitive === true
+      ? propertyDescriptor.describePrimitive(keyDescriptor, valueDescriptor)
+      : propertyDescriptor.describeComplex(keyDescriptor, valueDescriptor)
+  }
+
+  return curriedComplex(value)
+}
+module.exports = describe
diff --git a/node_modules/concordance/lib/diff.js b/node_modules/concordance/lib/diff.js
new file mode 100644
index 000000000..16191143f
--- /dev/null
+++ b/node_modules/concordance/lib/diff.js
@@ -0,0 +1,391 @@
+'use strict'
+
+const constants = require('./constants')
+const describe = require('./describe')
+const lineBuilder = require('./lineBuilder')
+const recursorUtils = require('./recursorUtils')
+const shouldCompareDeep = require('./shouldCompareDeep')
+const symbolProperties = require('./symbolProperties')
+const themeUtils = require('./themeUtils')
+const Circular = require('./Circular')
+const Indenter = require('./Indenter')
+
+const AMBIGUOUS = constants.AMBIGUOUS
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+const NOOP = Symbol('NOOP')
+
+const alwaysFormat = () => true
+
+function compareComplexShape (lhs, rhs) {
+  let result = lhs.compare(rhs)
+  if (result === DEEP_EQUAL) return DEEP_EQUAL
+  if (result === UNEQUAL || !shouldCompareDeep(result, lhs, rhs)) return UNEQUAL
+
+  let collectedSymbolProperties = false
+  let lhsRecursor = lhs.createRecursor()
+  let rhsRecursor = rhs.createRecursor()
+
+  do {
+    lhs = lhsRecursor()
+    rhs = rhsRecursor()
+
+    if (lhs === null && rhs === null) return SHALLOW_EQUAL
+    if (lhs === null || rhs === null) return UNEQUAL
+
+    result = lhs.compare(rhs)
+    if (result === UNEQUAL) return UNEQUAL
+    if (
+      result === AMBIGUOUS &&
+      lhs.isProperty === true && !collectedSymbolProperties &&
+      shouldCompareDeep(result, lhs, rhs)
+    ) {
+      collectedSymbolProperties = true
+      const lhsCollector = new symbolProperties.Collector(lhs, lhsRecursor)
+      const rhsCollector = new symbolProperties.Collector(rhs, rhsRecursor)
+
+      lhsRecursor = recursorUtils.sequence(
+        lhsCollector.createRecursor(),
+        recursorUtils.unshift(lhsRecursor, lhsCollector.collectAll()))
+      rhsRecursor = recursorUtils.sequence(
+        rhsCollector.createRecursor(),
+        recursorUtils.unshift(rhsRecursor, rhsCollector.collectAll()))
+    }
+  } while (true)
+}
+
+function diffDescriptors (lhs, rhs, options) {
+  const theme = themeUtils.normalize(options)
+  const invert = options ? options.invert === true : false
+
+  const lhsCircular = new Circular()
+  const rhsCircular = new Circular()
+  const maxDepth = (options && options.maxDepth) || 0
+
+  let indent = new Indenter(0, '  ')
+
+  const lhsStack = []
+  const rhsStack = []
+  let topIndex = -1
+
+  const buffer = lineBuilder.buffer()
+  const diffStack = []
+  let diffIndex = -1
+
+  const isCircular = descriptor => lhsCircular.has(descriptor) || rhsCircular.has(descriptor)
+
+  const format = (builder, subject, circular) => {
+    if (diffIndex >= 0 && !diffStack[diffIndex].shouldFormat(subject)) return
+
+    if (circular.has(subject)) {
+      diffStack[diffIndex].formatter.append(builder.single(theme.circular))
+      return
+    }
+
+    const formatStack = []
+    let formatIndex = -1
+
+    do {
+      if (circular.has(subject)) {
+        formatStack[formatIndex].formatter.append(builder.single(theme.circular), subject)
+      } else {
+        let didFormat = false
+        if (typeof subject.formatDeep === 'function') {
+          let formatted = subject.formatDeep(themeUtils.applyModifiers(subject, theme), indent)
+          if (formatted !== null) {
+            didFormat = true
+
+            if (formatIndex === -1) {
+              formatted = builder.setDefaultGutter(formatted)
+              if (diffIndex === -1) {
+                buffer.append(formatted)
+              } else {
+                diffStack[diffIndex].formatter.append(formatted, subject)
+              }
+            } else {
+              formatStack[formatIndex].formatter.append(formatted, subject)
+            }
+          }
+        }
+
+        if (!didFormat && typeof subject.formatShallow === 'function') {
+          const formatter = subject.formatShallow(themeUtils.applyModifiers(subject, theme), indent)
+          const recursor = subject.createRecursor()
+
+          if (formatter.increaseIndent && maxDepth > 0 && indent.level === maxDepth) {
+            const isEmpty = recursor() === null
+            let formatted = !isEmpty && typeof formatter.maxDepth === 'function'
+              ? formatter.maxDepth()
+              : formatter.finalize()
+
+            if (formatIndex === -1) {
+              formatted = builder.setDefaultGutter(formatted)
+              diffStack[diffIndex].formatter.append(formatted, subject)
+            } else {
+              formatStack[formatIndex].formatter.append(formatted, subject)
+            }
+          } else {
+            formatStack.push({
+              formatter,
+              recursor,
+              decreaseIndent: formatter.increaseIndent,
+              shouldFormat: formatter.shouldFormat || alwaysFormat,
+              subject
+            })
+            formatIndex++
+
+            if (formatter.increaseIndent) indent = indent.increase()
+            circular.add(subject)
+          }
+        }
+      }
+
+      while (formatIndex >= 0) {
+        do {
+          subject = formatStack[formatIndex].recursor()
+        } while (subject && !formatStack[formatIndex].shouldFormat(subject))
+
+        if (subject) {
+          break
+        }
+
+        const record = formatStack.pop()
+        formatIndex--
+        if (record.decreaseIndent) indent = indent.decrease()
+        circular.delete(record.subject)
+
+        let formatted = record.formatter.finalize()
+        if (formatIndex === -1) {
+          formatted = builder.setDefaultGutter(formatted)
+          if (diffIndex === -1) {
+            buffer.append(formatted)
+          } else {
+            diffStack[diffIndex].formatter.append(formatted, record.subject)
+          }
+        } else {
+          formatStack[formatIndex].formatter.append(formatted, record.subject)
+        }
+      }
+    } while (formatIndex >= 0)
+  }
+
+  do {
+    let compareResult = NOOP
+    if (lhsCircular.has(lhs)) {
+      compareResult = lhsCircular.get(lhs) === rhsCircular.get(rhs)
+        ? DEEP_EQUAL
+        : UNEQUAL
+    } else if (rhsCircular.has(rhs)) {
+      compareResult = UNEQUAL
+    }
+
+    let firstPassSymbolProperty = false
+    if (lhs.isProperty === true) {
+      compareResult = lhs.compare(rhs)
+      if (compareResult === AMBIGUOUS) {
+        const parent = lhsStack[topIndex].subject
+        firstPassSymbolProperty = parent.isSymbolPropertiesCollector !== true && parent.isSymbolPropertiesComparable !== true
+      }
+    }
+
+    let didFormat = false
+    let mustRecurse = false
+    if (compareResult !== DEEP_EQUAL && !firstPassSymbolProperty && typeof lhs.prepareDiff === 'function') {
+      const lhsRecursor = topIndex === -1 ? null : lhsStack[topIndex].recursor
+      const rhsRecursor = topIndex === -1 ? null : rhsStack[topIndex].recursor
+
+      const instructions = lhs.prepareDiff(
+        rhs,
+        lhsRecursor,
+        rhsRecursor,
+        compareComplexShape,
+        isCircular)
+
+      if (instructions !== null) {
+        if (topIndex >= 0) {
+          if (typeof instructions.lhsRecursor === 'function') {
+            lhsStack[topIndex].recursor = instructions.lhsRecursor
+          }
+          if (typeof instructions.rhsRecursor === 'function') {
+            rhsStack[topIndex].recursor = instructions.rhsRecursor
+          }
+        }
+
+        if (instructions.compareResult) {
+          compareResult = instructions.compareResult
+        }
+        if (instructions.mustRecurse === true) {
+          mustRecurse = true
+        } else {
+          if (instructions.actualIsExtraneous === true) {
+            format(lineBuilder.actual, lhs, lhsCircular)
+            didFormat = true
+          } else if (instructions.multipleAreExtraneous === true) {
+            for (const extraneous of instructions.descriptors) {
+              format(lineBuilder.actual, extraneous, lhsCircular)
+            }
+            didFormat = true
+          } else if (instructions.expectedIsMissing === true) {
+            format(lineBuilder.expected, rhs, rhsCircular)
+            didFormat = true
+          } else if (instructions.multipleAreMissing === true) {
+            for (const missing of instructions.descriptors) {
+              format(lineBuilder.expected, missing, rhsCircular)
+            }
+            didFormat = true
+          } else if (instructions.isUnequal === true) {
+            format(lineBuilder.actual, lhs, lhsCircular)
+            format(lineBuilder.expected, rhs, rhsCircular)
+            didFormat = true
+          } else if (!instructions.compareResult) {
+            // TODO: Throw a useful, custom error
+            throw new Error('Illegal result of prepareDiff()')
+          }
+        }
+      }
+    }
+
+    if (!didFormat) {
+      if (compareResult === NOOP) {
+        compareResult = lhs.compare(rhs)
+      }
+
+      if (!mustRecurse) {
+        mustRecurse = shouldCompareDeep(compareResult, lhs, rhs)
+      }
+
+      if (compareResult === DEEP_EQUAL) {
+        format(lineBuilder, lhs, lhsCircular)
+      } else if (mustRecurse) {
+        if (compareResult === AMBIGUOUS && lhs.isProperty === true) {
+          // Replace both sides by a pseudo-descriptor which collects symbol
+          // properties instead.
+          lhs = new symbolProperties.Collector(lhs, lhsStack[topIndex].recursor)
+          rhs = new symbolProperties.Collector(rhs, rhsStack[topIndex].recursor)
+          // Replace the current recursors so they can continue correctly after
+          // the collectors have been "compared". This is necessary since the
+          // collectors eat the first value after the last symbol property.
+          lhsStack[topIndex].recursor = recursorUtils.unshift(lhsStack[topIndex].recursor, lhs.collectAll())
+          rhsStack[topIndex].recursor = recursorUtils.unshift(rhsStack[topIndex].recursor, rhs.collectAll())
+        }
+
+        if (typeof lhs.diffShallow === 'function') {
+          const formatter = lhs.diffShallow(rhs, themeUtils.applyModifiers(lhs, theme), indent)
+          diffStack.push({
+            formatter,
+            origin: lhs,
+            decreaseIndent: formatter.increaseIndent,
+            exceedsMaxDepth: formatter.increaseIndent && maxDepth > 0 && indent.level >= maxDepth,
+            shouldFormat: formatter.shouldFormat || alwaysFormat
+          })
+          diffIndex++
+
+          if (formatter.increaseIndent) indent = indent.increase()
+        } else if (typeof lhs.formatShallow === 'function') {
+          const formatter = lhs.formatShallow(themeUtils.applyModifiers(lhs, theme), indent)
+          diffStack.push({
+            formatter,
+            decreaseIndent: formatter.increaseIndent,
+            exceedsMaxDepth: formatter.increaseIndent && maxDepth > 0 && indent.level >= maxDepth,
+            shouldFormat: formatter.shouldFormat || alwaysFormat,
+            subject: lhs
+          })
+          diffIndex++
+
+          if (formatter.increaseIndent) indent = indent.increase()
+        }
+
+        lhsCircular.add(lhs)
+        rhsCircular.add(rhs)
+
+        lhsStack.push({ diffIndex, subject: lhs, recursor: lhs.createRecursor() })
+        rhsStack.push({ diffIndex, subject: rhs, recursor: rhs.createRecursor() })
+        topIndex++
+      } else {
+        const diffed = typeof lhs.diffDeep === 'function'
+          ? lhs.diffDeep(rhs, themeUtils.applyModifiers(lhs, theme), indent)
+          : null
+
+        if (diffed === null) {
+          format(lineBuilder.actual, lhs, lhsCircular)
+          format(lineBuilder.expected, rhs, rhsCircular)
+        } else {
+          if (diffIndex === -1) {
+            buffer.append(diffed)
+          } else {
+            diffStack[diffIndex].formatter.append(diffed, lhs)
+          }
+        }
+      }
+    }
+
+    while (topIndex >= 0) {
+      lhs = lhsStack[topIndex].recursor()
+      rhs = rhsStack[topIndex].recursor()
+
+      if (lhs !== null && rhs !== null) {
+        break
+      }
+
+      if (lhs === null && rhs === null) {
+        const lhsRecord = lhsStack.pop()
+        const rhsRecord = rhsStack.pop()
+        lhsCircular.delete(lhsRecord.subject)
+        rhsCircular.delete(rhsRecord.subject)
+        topIndex--
+
+        if (lhsRecord.diffIndex === diffIndex) {
+          const record = diffStack.pop()
+          diffIndex--
+          if (record.decreaseIndent) indent = indent.decrease()
+
+          let formatted = record.formatter.finalize()
+          if (record.exceedsMaxDepth && !formatted.hasGutter) {
+            // The record exceeds the max depth, but contains no actual diff.
+            // Discard the potentially deep formatting and format just the
+            // original subject.
+            const subject = lhsRecord.subject
+            const formatter = subject.formatShallow(themeUtils.applyModifiers(subject, theme), indent)
+            const isEmpty = subject.createRecursor()() === null
+            formatted = !isEmpty && typeof formatter.maxDepth === 'function'
+              ? formatter.maxDepth()
+              : formatter.finalize()
+          }
+
+          if (diffIndex === -1) {
+            buffer.append(formatted)
+          } else {
+            diffStack[diffIndex].formatter.append(formatted, record.subject)
+          }
+        }
+      } else {
+        let builder, circular, stack, subject
+        if (lhs === null) {
+          builder = lineBuilder.expected
+          circular = rhsCircular
+          stack = rhsStack
+          subject = rhs
+        } else {
+          builder = lineBuilder.actual
+          circular = lhsCircular
+          stack = lhsStack
+          subject = lhs
+        }
+
+        do {
+          format(builder, subject, circular)
+          subject = stack[topIndex].recursor()
+        } while (subject !== null)
+      }
+    }
+  } while (topIndex >= 0)
+
+  return buffer.toString({diff: true, invert, theme})
+}
+exports.diffDescriptors = diffDescriptors
+
+function diff (actual, expected, options) {
+  return diffDescriptors(describe(actual, options), describe(expected, options), options)
+}
+exports.diff = diff
diff --git a/node_modules/concordance/lib/encoder.js b/node_modules/concordance/lib/encoder.js
new file mode 100644
index 000000000..ea1be3855
--- /dev/null
+++ b/node_modules/concordance/lib/encoder.js
@@ -0,0 +1,293 @@
+'use strict'
+
+const flattenDeep = require('lodash.flattendeep')
+
+// Indexes are hexadecimal to make reading the binary output easier.
+const valueTypes = {
+  zero: 0x00,
+  int8: 0x01,  // Note that the hex value equals the number of bytes required
+  int16: 0x02, // to store the integer.
+  int24: 0x03,
+  int32: 0x04,
+  int40: 0x05,
+  int48: 0x06,
+  // Leave room for int56 and int64
+  numberString: 0x09,
+  negativeZero: 0x0A,
+  notANumber: 0x0B,
+  infinity: 0x0C,
+  negativeInfinity: 0x0D,
+  undefined: 0x0E,
+  null: 0x0F,
+  true: 0x10,
+  false: 0x11,
+  utf8: 0x12,
+  bytes: 0x13,
+  list: 0x14,
+  descriptor: 0x15
+}
+
+const descriptorSymbol = Symbol('descriptor')
+exports.descriptorSymbol = descriptorSymbol
+
+function encodeInteger (type, value) {
+  const encoded = Buffer.alloc(type)
+  encoded.writeIntLE(value, 0, type)
+  return [type, encoded]
+}
+
+function encodeValue (value) {
+  if (Object.is(value, 0)) return valueTypes.zero
+  if (Object.is(value, -0)) return valueTypes.negativeZero
+  if (Object.is(value, NaN)) return valueTypes.notANumber
+  if (value === Infinity) return valueTypes.infinity
+  if (value === -Infinity) return valueTypes.negativeInfinity
+  if (value === undefined) return valueTypes.undefined
+  if (value === null) return valueTypes.null
+  if (value === true) return valueTypes.true
+  if (value === false) return valueTypes.false
+
+  const type = typeof value
+  if (type === 'number') {
+    if (Number.isInteger(value)) {
+      // The integer types are signed, so int8 can only store 7 bits, int16
+      // only 15, etc.
+      if (value >= -0x80 && value < 0x80) return encodeInteger(valueTypes.int8, value)
+      if (value >= -0x8000 && value < 0x8000) return encodeInteger(valueTypes.int16, value)
+      if (value >= -0x800000 && value < 0x800000) return encodeInteger(valueTypes.int24, value)
+      if (value >= -0x80000000 && value < 0x80000000) return encodeInteger(valueTypes.int32, value)
+      if (value >= -0x8000000000 && value < 0x8000000000) return encodeInteger(valueTypes.int40, value)
+      if (value >= -0x800000000000 && value < 0x800000000000) return encodeInteger(valueTypes.int48, value)
+      // Fall through to encoding the value as a number string.
+    }
+
+    const encoded = Buffer.from(String(value), 'utf8')
+    return [valueTypes.numberString, encodeValue(encoded.length), encoded]
+  }
+
+  if (type === 'string') {
+    const encoded = Buffer.from(value, 'utf8')
+    return [valueTypes.utf8, encodeValue(encoded.length), encoded]
+  }
+
+  if (Buffer.isBuffer(value)) {
+    return [valueTypes.bytes, encodeValue(value.byteLength), value]
+  }
+
+  if (Array.isArray(value)) {
+    return [
+      value[descriptorSymbol] === true ? valueTypes.descriptor : valueTypes.list,
+      encodeValue(value.length),
+      value.map(encodeValue)
+    ]
+  }
+
+  const hex = `0x${type.toString(16).toUpperCase()}`
+  throw new TypeError(`Unexpected value with type ${hex}`)
+}
+
+function decodeValue (buffer, byteOffset) {
+  const type = buffer.readUInt8(byteOffset)
+  byteOffset += 1
+
+  if (type === valueTypes.zero) return { byteOffset, value: 0 }
+  if (type === valueTypes.negativeZero) return { byteOffset, value: -0 }
+  if (type === valueTypes.notANumber) return { byteOffset, value: NaN }
+  if (type === valueTypes.infinity) return { byteOffset, value: Infinity }
+  if (type === valueTypes.negativeInfinity) return { byteOffset, value: -Infinity }
+  if (type === valueTypes.undefined) return { byteOffset, value: undefined }
+  if (type === valueTypes.null) return { byteOffset, value: null }
+  if (type === valueTypes.true) return { byteOffset, value: true }
+  if (type === valueTypes.false) return { byteOffset, value: false }
+
+  if (
+    type === valueTypes.int8 || type === valueTypes.int16 || type === valueTypes.int24 ||
+    type === valueTypes.int32 || type === valueTypes.int40 || type === valueTypes.int48
+  ) {
+    const value = buffer.readIntLE(byteOffset, type)
+    byteOffset += type
+    return { byteOffset, value }
+  }
+
+  if (type === valueTypes.numberString || type === valueTypes.utf8 || type === valueTypes.bytes) {
+    const length = decodeValue(buffer, byteOffset)
+    const start = length.byteOffset
+    const end = start + length.value
+
+    if (type === valueTypes.numberString) {
+      const value = Number(buffer.toString('utf8', start, end))
+      return { byteOffset: end, value }
+    }
+
+    if (type === valueTypes.utf8) {
+      const value = buffer.toString('utf8', start, end)
+      return { byteOffset: end, value }
+    }
+
+    const value = buffer.slice(start, end)
+    return { byteOffset: end, value }
+  }
+
+  if (type === valueTypes.list || type === valueTypes.descriptor) {
+    const length = decodeValue(buffer, byteOffset)
+    byteOffset = length.byteOffset
+
+    const value = new Array(length.value)
+    if (type === valueTypes.descriptor) {
+      value[descriptorSymbol] = true
+    }
+
+    for (let index = 0; index < length.value; index++) {
+      const item = decodeValue(buffer, byteOffset)
+      byteOffset = item.byteOffset
+      value[index] = item.value
+    }
+
+    return { byteOffset, value }
+  }
+
+  const hex = `0x${type.toString(16).toUpperCase()}`
+  throw new TypeError(`Could not decode type ${hex}`)
+}
+
+function buildBuffer (numberOrArray) {
+  if (typeof numberOrArray === 'number') {
+    const byte = Buffer.alloc(1)
+    byte.writeUInt8(numberOrArray)
+    return byte
+  }
+
+  const array = flattenDeep(numberOrArray)
+  const buffers = new Array(array.length)
+  let byteLength = 0
+  for (let index = 0; index < array.length; index++) {
+    if (typeof array[index] === 'number') {
+      byteLength += 1
+      const byte = Buffer.alloc(1)
+      byte.writeUInt8(array[index])
+      buffers[index] = byte
+    } else {
+      byteLength += array[index].byteLength
+      buffers[index] = array[index]
+    }
+  }
+  return Buffer.concat(buffers, byteLength)
+}
+
+function encode (serializerVersion, rootRecord, usedPlugins) {
+  const buffers = []
+  let byteOffset = 0
+
+  const versionHeader = Buffer.alloc(2)
+  versionHeader.writeUInt16LE(serializerVersion)
+  buffers.push(versionHeader)
+  byteOffset += versionHeader.byteLength
+
+  const rootOffset = Buffer.alloc(4)
+  buffers.push(rootOffset)
+  byteOffset += rootOffset.byteLength
+
+  const numPlugins = buildBuffer(encodeValue(usedPlugins.size))
+  buffers.push(numPlugins)
+  byteOffset += numPlugins.byteLength
+
+  for (const name of usedPlugins.keys()) {
+    const plugin = usedPlugins.get(name)
+    const record = buildBuffer([
+      encodeValue(name),
+      encodeValue(plugin.serializerVersion)
+    ])
+    buffers.push(record)
+    byteOffset += record.byteLength
+  }
+
+  const queue = [rootRecord]
+  const pointers = [rootOffset]
+  while (queue.length > 0) {
+    pointers.shift().writeUInt32LE(byteOffset, 0)
+
+    const record = queue.shift()
+    const recordHeader = buildBuffer([
+      encodeValue(record.pluginIndex),
+      encodeValue(record.id),
+      encodeValue(record.children.length)
+    ])
+    buffers.push(recordHeader)
+    byteOffset += recordHeader.byteLength
+
+    // Add pointers before encoding the state. This allows, if it ever becomes
+    // necessary, for records to be extracted from a buffer without having to
+    // parse the (variable length) state field.
+    for (const child of record.children) {
+      queue.push(child)
+
+      const pointer = Buffer.alloc(4)
+      pointers.push(pointer)
+      buffers.push(pointer)
+      byteOffset += 4
+    }
+
+    const state = buildBuffer(encodeValue(record.state))
+    buffers.push(state)
+    byteOffset += state.byteLength
+  }
+
+  return Buffer.concat(buffers, byteOffset)
+}
+exports.encode = encode
+
+function decodePlugins (buffer) {
+  const $numPlugins = decodeValue(buffer, 0)
+  let byteOffset = $numPlugins.byteOffset
+
+  const usedPlugins = new Map()
+  const lastIndex = $numPlugins.value
+  for (let index = 1; index <= lastIndex; index++) {
+    const $name = decodeValue(buffer, byteOffset)
+    const name = $name.value
+    byteOffset = $name.byteOffset
+
+    const serializerVersion = decodeValue(buffer, byteOffset).value
+    usedPlugins.set(index, {name, serializerVersion})
+  }
+
+  return usedPlugins
+}
+exports.decodePlugins = decodePlugins
+
+function decodeRecord (buffer, byteOffset) {
+  const $pluginIndex = decodeValue(buffer, byteOffset)
+  const pluginIndex = $pluginIndex.value
+  byteOffset = $pluginIndex.byteOffset
+
+  const $id = decodeValue(buffer, byteOffset)
+  const id = $id.value
+  byteOffset = $id.byteOffset
+
+  const $numPointers = decodeValue(buffer, byteOffset)
+  const numPointers = $numPointers.value
+  byteOffset = $numPointers.byteOffset
+
+  const pointerAddresses = new Array(numPointers)
+  for (let index = 0; index < numPointers; index++) {
+    pointerAddresses[index] = buffer.readUInt32LE(byteOffset)
+    byteOffset += 4
+  }
+
+  const state = decodeValue(buffer, byteOffset).value
+  return {id, pluginIndex, state, pointerAddresses}
+}
+exports.decodeRecord = decodeRecord
+
+function extractVersion (buffer) {
+  return buffer.readUInt16LE(0)
+}
+exports.extractVersion = extractVersion
+
+function decode (buffer) {
+  const rootOffset = buffer.readUInt32LE(2)
+  const pluginBuffer = buffer.slice(6, rootOffset)
+  const rootRecord = decodeRecord(buffer, rootOffset)
+  return {pluginBuffer, rootRecord}
+}
+exports.decode = decode
diff --git a/node_modules/concordance/lib/format.js b/node_modules/concordance/lib/format.js
new file mode 100644
index 000000000..7629579d7
--- /dev/null
+++ b/node_modules/concordance/lib/format.js
@@ -0,0 +1,101 @@
+'use strict'
+
+const describe = require('./describe')
+const lineBuilder = require('./lineBuilder')
+const themeUtils = require('./themeUtils')
+const Circular = require('./Circular')
+const Indenter = require('./Indenter')
+
+const alwaysFormat = () => true
+const fixedIndent = new Indenter(0, '  ')
+
+function formatDescriptor (subject, options) {
+  const theme = themeUtils.normalize(options)
+  if (subject.isPrimitive === true) {
+    const formatted = subject.formatDeep(themeUtils.applyModifiers(subject, theme), fixedIndent)
+    return formatted.toString({diff: false})
+  }
+
+  const circular = new Circular()
+  const maxDepth = (options && options.maxDepth) || 0
+
+  let indent = fixedIndent
+
+  const buffer = lineBuilder.buffer()
+  const stack = []
+  let topIndex = -1
+
+  do {
+    if (circular.has(subject)) {
+      stack[topIndex].formatter.append(lineBuilder.single(theme.circular), subject)
+    } else {
+      let didFormat = false
+      if (typeof subject.formatDeep === 'function') {
+        const formatted = subject.formatDeep(themeUtils.applyModifiers(subject, theme), indent)
+        if (formatted !== null) {
+          didFormat = true
+          if (topIndex === -1) {
+            buffer.append(formatted)
+          } else {
+            stack[topIndex].formatter.append(formatted, subject)
+          }
+        }
+      }
+
+      if (!didFormat && typeof subject.formatShallow === 'function') {
+        const formatter = subject.formatShallow(themeUtils.applyModifiers(subject, theme), indent)
+        const recursor = subject.createRecursor()
+
+        if (formatter.increaseIndent && maxDepth > 0 && indent.level === maxDepth) {
+          const isEmpty = recursor() === null
+          const formatted = !isEmpty && typeof formatter.maxDepth === 'function'
+            ? formatter.maxDepth()
+            : formatter.finalize()
+          stack[topIndex].formatter.append(formatted, subject)
+        } else {
+          stack.push({
+            formatter,
+            recursor,
+            decreaseIndent: formatter.increaseIndent,
+            shouldFormat: formatter.shouldFormat || alwaysFormat,
+            subject
+          })
+          topIndex++
+
+          if (formatter.increaseIndent) indent = indent.increase()
+          circular.add(subject)
+        }
+      }
+    }
+
+    while (topIndex >= 0) {
+      do {
+        subject = stack[topIndex].recursor()
+      } while (subject && !stack[topIndex].shouldFormat(subject))
+
+      if (subject) {
+        break
+      }
+
+      const record = stack.pop()
+      topIndex--
+      if (record.decreaseIndent) indent = indent.decrease()
+      circular.delete(record.subject)
+
+      const formatted = record.formatter.finalize()
+      if (topIndex === -1) {
+        buffer.append(formatted)
+      } else {
+        stack[topIndex].formatter.append(formatted, record.subject)
+      }
+    }
+  } while (topIndex >= 0)
+
+  return buffer.toString({diff: false})
+}
+exports.formatDescriptor = formatDescriptor
+
+function format (value, options) {
+  return formatDescriptor(describe(value, options), options)
+}
+exports.format = format
diff --git a/node_modules/concordance/lib/formatUtils.js b/node_modules/concordance/lib/formatUtils.js
new file mode 100644
index 000000000..07e8b2c57
--- /dev/null
+++ b/node_modules/concordance/lib/formatUtils.js
@@ -0,0 +1,123 @@
+'use strict'
+
+const lineBuilder = require('./lineBuilder')
+
+function wrap (fromTheme, value) {
+  return fromTheme.open + value + fromTheme.close
+}
+exports.wrap = wrap
+
+function formatCtorAndStringTag (theme, object) {
+  if (!object.ctor) return wrap(theme.object.stringTag, object.stringTag)
+
+  let retval = wrap(theme.object.ctor, object.ctor)
+  if (object.stringTag && object.stringTag !== object.ctor && object.stringTag !== 'Object') {
+    retval += ' ' + wrap(theme.object.secondaryStringTag, object.stringTag)
+  }
+  return retval
+}
+exports.formatCtorAndStringTag = formatCtorAndStringTag
+
+class ObjectFormatter {
+  constructor (object, theme, indent) {
+    this.object = object
+    this.theme = theme
+    this.indent = indent
+
+    this.increaseIndent = true
+
+    this.innerLines = lineBuilder.buffer()
+    this.pendingStats = null
+  }
+
+  append (formatted, origin) {
+    if (origin.isStats === true) {
+      this.pendingStats = formatted
+    } else {
+      if (this.pendingStats !== null) {
+        if (!this.innerLines.isEmpty) {
+          this.innerLines.append(this.pendingStats)
+        }
+        this.pendingStats = null
+      }
+      this.innerLines.append(formatted)
+    }
+  }
+
+  finalize () {
+    const variant = this.object.isList
+      ? this.theme.list
+      : this.theme.object
+
+    const ctor = this.object.ctor
+    const stringTag = this.object.stringTag
+    const prefix = (ctor === 'Array' || ctor === 'Object') && ctor === stringTag
+      ? ''
+      : formatCtorAndStringTag(this.theme, this.object) + ' '
+
+    if (this.innerLines.isEmpty) {
+      return lineBuilder.single(prefix + variant.openBracket + variant.closeBracket)
+    }
+
+    return lineBuilder.first(prefix + variant.openBracket)
+      .concat(this.innerLines.withFirstPrefixed(this.indent.increase()).stripFlags())
+      .append(lineBuilder.last(this.indent + variant.closeBracket))
+  }
+
+  maxDepth () {
+    const variant = this.object.isList
+      ? this.theme.list
+      : this.theme.object
+
+    return lineBuilder.single(
+      formatCtorAndStringTag(this.theme, this.object) + ' ' + variant.openBracket +
+      ' ' + this.theme.maxDepth + ' ' + variant.closeBracket)
+  }
+
+  shouldFormat () {
+    return true
+  }
+
+  customize (methods) {
+    if (methods.finalize) {
+      this.finalize = () => methods.finalize(this.innerLines)
+    }
+    if (methods.maxDepth) {
+      this.maxDepth = methods.maxDepth
+    }
+    if (methods.shouldFormat) {
+      this.shouldFormat = methods.shouldFormat
+    }
+
+    return this
+  }
+}
+exports.ObjectFormatter = ObjectFormatter
+
+class SingleValueFormatter {
+  constructor (theme, finalizeFn, increaseIndent) {
+    this.theme = theme
+    this.finalizeFn = finalizeFn
+    this.hasValue = false
+    this.increaseIndent = increaseIndent === true
+    this.value = null
+  }
+
+  append (formatted) {
+    if (this.hasValue) throw new Error('Formatter buffer can only take one formatted value.')
+
+    this.hasValue = true
+    this.value = formatted
+  }
+
+  finalize () {
+    if (!this.hasValue) throw new Error('Formatter buffer never received a formatted value.')
+
+    return this.finalizeFn(this.value)
+  }
+
+  maxDepth () {
+    return this.finalizeFn(lineBuilder.single(this.theme.maxDepth))
+  }
+}
+exports.SingleValueFormatter = SingleValueFormatter
diff --git a/node_modules/concordance/lib/getCtor.js b/node_modules/concordance/lib/getCtor.js
new file mode 100644
index 000000000..4bbdfd158
--- /dev/null
+++ b/node_modules/concordance/lib/getCtor.js
@@ -0,0 +1,43 @@
+'use strict'
+
+const hop = Object.prototype.hasOwnProperty
+
+function getCtor (stringTag, value) {
+  if (value.constructor) {
+    const name = value.constructor.name
+    return typeof name === 'string' && name !== ''
+      ? name
+      : null
+  }
+
+  if (value.constructor === undefined) {
+    if (stringTag !== 'Object' || value instanceof Object) return null
+
+    // Values without a constructor, that do not inherit from `Object`, but are
+    // tagged as objects, may come from `Object.create(null)`. Or they can come
+    // from a different realm, e.g.:
+    //
+    // ```
+    // require('vm').runInNewContext(`
+    //   const Foo = function () {}
+    //   Foo.prototype.constructor = undefined
+    //   return new Foo()
+    // `)
+    // ```
+    //
+    // Treat such objects as if they came from `Object.create(null)` (in the
+    // current realm) only if they do not have inherited properties. This allows
+    // these objects to be compared with object literals.
+    //
+    // This means `Object.create(null)` is not differentiated from `{}`.
+
+    // Using `const` prevents Crankshaft optimizations
+    for (var p in value) { // eslint-disable-line no-var
+      if (!hop.call(value, p)) return null
+    }
+    return stringTag
+  }
+
+  return null
+}
+module.exports = getCtor
diff --git a/node_modules/concordance/lib/getObjectKeys.js b/node_modules/concordance/lib/getObjectKeys.js
new file mode 100644
index 000000000..4b0c3e368
--- /dev/null
+++ b/node_modules/concordance/lib/getObjectKeys.js
@@ -0,0 +1,36 @@
+'use strict'
+
+function getObjectKeys (obj, excludeListItemAccessorsBelowLength) {
+  const keys = []
+  let size = 0
+
+  // Sort property names, they should never be order-sensitive
+  const nameCandidates = Object.getOwnPropertyNames(obj).sort()
+  // Comparators should verify symbols in an order-insensitive manner if
+  // possible.
+  const symbolCandidates = Object.getOwnPropertySymbols(obj)
+
+  for (let i = 0; i < nameCandidates.length; i++) {
+    const name = nameCandidates[i]
+
+    let accept = true
+    if (excludeListItemAccessorsBelowLength > 0) {
+      const index = Number(name)
+      accept = (index % 1 !== 0) || index >= excludeListItemAccessorsBelowLength
+    }
+
+    if (accept && Object.getOwnPropertyDescriptor(obj, name).enumerable) {
+      keys[size++] = name
+    }
+  }
+
+  for (let i = 0; i < symbolCandidates.length; i++) {
+    const symbol = symbolCandidates[i]
+    if (Object.getOwnPropertyDescriptor(obj, symbol).enumerable) {
+      keys[size++] = symbol
+    }
+  }
+
+  return { keys, size }
+}
+module.exports = getObjectKeys
diff --git a/node_modules/concordance/lib/getStringTag.js b/node_modules/concordance/lib/getStringTag.js
new file mode 100644
index 000000000..994ec4bec
--- /dev/null
+++ b/node_modules/concordance/lib/getStringTag.js
@@ -0,0 +1,30 @@
+'use strict'
+
+const ts = Object.prototype.toString
+function getStringTag (value) {
+  return ts.call(value).slice(8, -1)
+}
+
+const fts = Function.prototype.toString
+const promiseCtorString = fts.call(Promise)
+const isPromise = value => {
+  if (!value.constructor) return false
+
+  try {
+    return fts.call(value.constructor) === promiseCtorString
+  } catch (err) {
+    return false
+  }
+}
+
+if (getStringTag(Promise.resolve()) === 'Promise') {
+  module.exports = getStringTag
+} else {
+  const getStringTagWithPromiseWorkaround = value => {
+    const stringTag = getStringTag(value)
+    return stringTag === 'Object' && isPromise(value)
+      ? 'Promise'
+      : stringTag
+  }
+  module.exports = getStringTagWithPromiseWorkaround
+}
diff --git a/node_modules/concordance/lib/hasLength.js b/node_modules/concordance/lib/hasLength.js
new file mode 100644
index 000000000..18df0d369
--- /dev/null
+++ b/node_modules/concordance/lib/hasLength.js
@@ -0,0 +1,7 @@
+'use strict'
+
+const hop = Object.prototype.hasOwnProperty
+function hasLength (obj) {
+  return Array.isArray(obj) || (hop.call(obj, 'length') && typeof obj.length === 'number')
+}
+module.exports = hasLength
diff --git a/node_modules/concordance/lib/isEnumerable.js b/node_modules/concordance/lib/isEnumerable.js
new file mode 100644
index 000000000..90c2df1e1
--- /dev/null
+++ b/node_modules/concordance/lib/isEnumerable.js
@@ -0,0 +1,7 @@
+'use strict'
+
+function isEnumerable (obj, key) {
+  const desc = Object.getOwnPropertyDescriptor(obj, key)
+  return desc && desc.enumerable
+}
+module.exports = isEnumerable
diff --git a/node_modules/concordance/lib/lineBuilder.js b/node_modules/concordance/lib/lineBuilder.js
new file mode 100644
index 000000000..934ac0095
--- /dev/null
+++ b/node_modules/concordance/lib/lineBuilder.js
@@ -0,0 +1,309 @@
+'use strict'
+
+const ACTUAL = Symbol('lineBuilder.gutters.ACTUAL')
+const EXPECTED = Symbol('lineBuilder.gutters.EXPECTED')
+
+function translateGutter (theme, invert, gutter) {
+  if (invert) {
+    if (gutter === ACTUAL) return theme.diffGutters.expected
+    if (gutter === EXPECTED) return theme.diffGutters.actual
+  } else {
+    if (gutter === ACTUAL) return theme.diffGutters.actual
+    if (gutter === EXPECTED) return theme.diffGutters.expected
+  }
+  return theme.diffGutters.padding
+}
+
+class Line {
+  constructor (isFirst, isLast, gutter, stringValue) {
+    this.isFirst = isFirst
+    this.isLast = isLast
+    this.gutter = gutter
+    this.stringValue = stringValue
+  }
+
+  * [Symbol.iterator] () {
+    yield this
+  }
+
+  get isEmpty () {
+    return false
+  }
+
+  get hasGutter () {
+    return this.gutter !== null
+  }
+
+  get isSingle () {
+    return this.isFirst && this.isLast
+  }
+
+  append (other) {
+    return this.concat(other)
+  }
+
+  concat (other) {
+    return new Collection()
+      .append(this)
+      .append(other)
+  }
+
+  toString (options) {
+    if (options.diff === false) return this.stringValue
+
+    return translateGutter(options.theme, options.invert, this.gutter) + this.stringValue
+  }
+
+  mergeWithInfix (infix, other) {
+    if (other.isLine !== true) {
+      return new Collection()
+        .append(this)
+        .mergeWithInfix(infix, other)
+    }
+
+    return new Line(this.isFirst, other.isLast, other.gutter, this.stringValue + infix + other.stringValue)
+  }
+
+  withFirstPrefixed (prefix) {
+    if (!this.isFirst) return this
+
+    return new Line(true, this.isLast, this.gutter, prefix + this.stringValue)
+  }
+
+  withLastPostfixed (postfix) {
+    if (!this.isLast) return this
+
+    return new Line(this.isFirst, true, this.gutter, this.stringValue + postfix)
+  }
+
+  stripFlags () {
+    return new Line(false, false, this.gutter, this.stringValue)
+  }
+
+  decompose () {
+    return new Collection()
+      .append(this)
+      .decompose()
+  }
+}
+Object.defineProperty(Line.prototype, 'isLine', {value: true})
+
+class Collection {
+  constructor () {
+    this.buffer = []
+  }
+
+  * [Symbol.iterator] () {
+    for (const appended of this.buffer) {
+      for (const line of appended) yield line
+    }
+  }
+
+  get isEmpty () {
+    return this.buffer.length === 0
+  }
+
+  get hasGutter () {
+    for (const line of this) {
+      if (line.hasGutter) return true
+    }
+    return false
+  }
+
+  get isSingle () {
+    const iterator = this[Symbol.iterator]()
+    iterator.next()
+    return iterator.next().done === true
+  }
+
+  append (lineOrLines) {
+    if (!lineOrLines.isEmpty) this.buffer.push(lineOrLines)
+    return this
+  }
+
+  concat (other) {
+    return new Collection()
+      .append(this)
+      .append(other)
+  }
+
+  toString (options) {
+    let lines = this
+
+    if (options.invert) {
+      lines = new Collection()
+      let buffer = new Collection()
+
+      let prev = null
+      for (const line of this) {
+        if (line.gutter === ACTUAL) {
+          if (prev !== null && prev.gutter !== ACTUAL && !buffer.isEmpty) {
+            lines.append(buffer)
+            buffer = new Collection()
+          }
+
+          buffer.append(line)
+        } else if (line.gutter === EXPECTED) {
+          lines.append(line)
+        } else {
+          if (!buffer.isEmpty) {
+            lines.append(buffer)
+            buffer = new Collection()
+          }
+
+          lines.append(line)
+        }
+
+        prev = line
+      }
+      lines.append(buffer)
+    }
+
+    return Array.from(lines, line => line.toString(options)).join('\n')
+  }
+
+  mergeWithInfix (infix, from) {
+    if (from.isEmpty) throw new Error('Cannot merge, `from` is empty.')
+
+    const otherLines = Array.from(from)
+    if (!otherLines[0].isFirst) throw new Error('Cannot merge, `from` has no first line.')
+
+    const merged = new Collection()
+    let seenLast = false
+    for (const line of this) {
+      if (seenLast) throw new Error('Cannot merge line, the last line has already been seen.')
+
+      if (!line.isLast) {
+        merged.append(line)
+        continue
+      }
+
+      seenLast = true
+      for (const other of otherLines) {
+        if (other.isFirst) {
+          merged.append(line.mergeWithInfix(infix, other))
+        } else {
+          merged.append(other)
+        }
+      }
+    }
+    return merged
+  }
+
+  withFirstPrefixed (prefix) {
+    return new Collection()
+      .append(Array.from(this, line => line.withFirstPrefixed(prefix)))
+  }
+
+  withLastPostfixed (postfix) {
+    return new Collection()
+      .append(Array.from(this, line => line.withLastPostfixed(postfix)))
+  }
+
+  stripFlags () {
+    return new Collection()
+      .append(Array.from(this, line => line.stripFlags()))
+  }
+
+  decompose () {
+    const first = {actual: new Collection(), expected: new Collection()}
+    const last = {actual: new Collection(), expected: new Collection()}
+    const remaining = new Collection()
+
+    for (const line of this) {
+      if (line.isFirst && line.gutter === ACTUAL) {
+        first.actual.append(line)
+      } else if (line.isFirst && line.gutter === EXPECTED) {
+        first.expected.append(line)
+      } else if (line.isLast && line.gutter === ACTUAL) {
+        last.actual.append(line)
+      } else if (line.isLast && line.gutter === EXPECTED) {
+        last.expected.append(line)
+      } else {
+        remaining.append(line)
+      }
+    }
+
+    return {first, last, remaining}
+  }
+}
+Object.defineProperty(Collection.prototype, 'isCollection', {value: true})
+
+function setDefaultGutter (iterable, gutter) {
+  return new Collection()
+    .append(Array.from(iterable, line => {
+      return line.gutter === null
+        ? new Line(line.isFirst, line.isLast, gutter, line.stringValue)
+        : line
+    }))
+}
+
+module.exports = {
+  buffer () {
+    return new Collection()
+  },
+
+  first (stringValue) {
+    return new Line(true, false, null, stringValue)
+  },
+
+  last (stringValue) {
+    return new Line(false, true, null, stringValue)
+  },
+
+  line (stringValue) {
+    return new Line(false, false, null, stringValue)
+  },
+
+  single (stringValue) {
+    return new Line(true, true, null, stringValue)
+  },
+
+  setDefaultGutter (lineOrCollection) {
+    return lineOrCollection
+  },
+
+  actual: {
+    first (stringValue) {
+      return new Line(true, false, ACTUAL, stringValue)
+    },
+
+    last (stringValue) {
+      return new Line(false, true, ACTUAL, stringValue)
+    },
+
+    line (stringValue) {
+      return new Line(false, false, ACTUAL, stringValue)
+    },
+
+    single (stringValue) {
+      return new Line(true, true, ACTUAL, stringValue)
+    },
+
+    setDefaultGutter (lineOrCollection) {
+      return setDefaultGutter(lineOrCollection, ACTUAL)
+    }
+  },
+
+  expected: {
+    first (stringValue) {
+      return new Line(true, false, EXPECTED, stringValue)
+    },
+
+    last (stringValue) {
+      return new Line(false, true, EXPECTED, stringValue)
+    },
+
+    line (stringValue) {
+      return new Line(false, false, EXPECTED, stringValue)
+    },
+
+    single (stringValue) {
+      return new Line(true, true, EXPECTED, stringValue)
+    },
+
+    setDefaultGutter (lineOrCollection) {
+      return setDefaultGutter(lineOrCollection, EXPECTED)
+    }
+  }
+}
diff --git a/node_modules/concordance/lib/metaDescriptors/item.js b/node_modules/concordance/lib/metaDescriptors/item.js
new file mode 100644
index 000000000..1539b624a
--- /dev/null
+++ b/node_modules/concordance/lib/metaDescriptors/item.js
@@ -0,0 +1,254 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const recursorUtils = require('../recursorUtils')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describeComplex (index, value) {
+  return new ComplexItem(index, value)
+}
+exports.describeComplex = describeComplex
+
+function deserializeComplex (index, recursor) {
+  const value = recursor()
+  return new ComplexItem(index, value)
+}
+exports.deserializeComplex = deserializeComplex
+
+function describePrimitive (index, value) {
+  return new PrimitiveItem(index, value)
+}
+exports.describePrimitive = describePrimitive
+
+function deserializePrimitive (state) {
+  const index = state[0]
+  const value = state[1]
+  return new PrimitiveItem(index, value)
+}
+exports.deserializePrimitive = deserializePrimitive
+
+const complexTag = Symbol('ComplexItem')
+exports.complexTag = complexTag
+
+const primitiveTag = Symbol('PrimitiveItem')
+exports.primitiveTag = primitiveTag
+
+class ComplexItem {
+  constructor (index, value) {
+    this.index = index
+    this.value = value
+  }
+
+  createRecursor () {
+    return recursorUtils.singleValue(this.value)
+  }
+
+  compare (expected) {
+    return expected.tag === complexTag && this.index === expected.index
+      ? this.value.compare(expected.value)
+      : UNEQUAL
+  }
+
+  formatShallow (theme, indent) {
+    const increaseValueIndent = theme.item.increaseValueIndent === true
+    return new formatUtils.SingleValueFormatter(theme, value => {
+      if (typeof theme.item.customFormat === 'function') {
+        return theme.item.customFormat(theme, indent, value)
+      }
+
+      return value.withLastPostfixed(theme.item.after)
+    }, increaseValueIndent)
+  }
+
+  prepareDiff (expected, lhsRecursor, rhsRecursor, compareComplexShape, isCircular) {
+    // Circular values cannot be compared. They must be treated as being unequal when diffing.
+    if (isCircular(this.value) || isCircular(expected.value)) return {compareResult: UNEQUAL}
+
+    // Try to line up this or remaining items with the expected items.
+    const lhsFork = recursorUtils.fork(lhsRecursor)
+    const rhsFork = recursorUtils.fork(rhsRecursor)
+    const initialExpected = expected
+
+    let expectedIsMissing = false
+    while (!expectedIsMissing && expected !== null && expected.isItem === true) {
+      if (expected.tag === complexTag) {
+        expectedIsMissing = compareComplexShape(this.value, expected.value) !== UNEQUAL
+      }
+
+      expected = rhsFork.shared()
+    }
+
+    let actualIsExtraneous = false
+    if (initialExpected.tag === complexTag) {
+      let actual = this
+      while (!actualIsExtraneous && actual !== null && actual.isItem === true) {
+        if (actual.tag === complexTag) {
+          actualIsExtraneous = compareComplexShape(actual.value, initialExpected.value) !== UNEQUAL
+        }
+
+        actual = lhsFork.shared()
+      }
+    } else if (initialExpected.tag === primitiveTag) {
+      let actual = this
+      while (!actualIsExtraneous && actual !== null && actual.isItem === true) {
+        if (actual.tag === primitiveTag) {
+          actualIsExtraneous = initialExpected.value.compare(actual.value) === DEEP_EQUAL
+        }
+
+        actual = lhsFork.shared()
+      }
+    }
+
+    if (actualIsExtraneous && !expectedIsMissing) {
+      return {
+        actualIsExtraneous: true,
+        lhsRecursor: lhsFork.recursor,
+        rhsRecursor: recursorUtils.map(
+          recursorUtils.unshift(rhsFork.recursor, initialExpected),
+          next => {
+            if (next.isItem !== true) return next
+
+            next.index++
+            return next
+          })
+      }
+    }
+
+    if (expectedIsMissing && !actualIsExtraneous) {
+      return {
+        expectedIsMissing: true,
+        lhsRecursor: recursorUtils.map(
+          recursorUtils.unshift(lhsFork.recursor, this),
+          next => {
+            if (next.isItem !== true) return next
+
+            next.index++
+            return next
+          }),
+        rhsRecursor: rhsFork.recursor
+      }
+    }
+
+    const mustRecurse = this.tag === complexTag && initialExpected.tag === complexTag &&
+      this.value.compare(initialExpected.value) !== UNEQUAL
+    return {
+      mustRecurse,
+      isUnequal: !mustRecurse,
+      lhsRecursor: lhsFork.recursor,
+      rhsRecursor: rhsFork.recursor
+    }
+  }
+
+  serialize () {
+    return this.index
+  }
+}
+Object.defineProperty(ComplexItem.prototype, 'isItem', { value: true })
+Object.defineProperty(ComplexItem.prototype, 'tag', { value: complexTag })
+
+class PrimitiveItem {
+  constructor (index, value) {
+    this.index = index
+    this.value = value
+  }
+
+  compare (expected) {
+    return expected.tag === primitiveTag && this.index === expected.index
+      ? this.value.compare(expected.value)
+      : UNEQUAL
+  }
+
+  formatDeep (theme, indent) {
+    const increaseValueIndent = theme.item.increaseValueIndent === true
+    const valueIndent = increaseValueIndent ? indent.increase() : indent
+
+    // Since the value is formatted directly, modifiers are not applied. Apply
+    // modifiers to the item descriptor instead.
+    const formatted = this.value.formatDeep(theme, valueIndent)
+
+    if (typeof theme.item.customFormat === 'function') {
+      return theme.item.customFormat(theme, indent, formatted)
+    }
+
+    return formatted.withLastPostfixed(theme.item.after)
+  }
+
+  prepareDiff (expected, lhsRecursor, rhsRecursor, compareComplexShape, isCircular) {
+    const compareResult = this.compare(expected)
+    // Short-circuit when values are deeply equal.
+    if (compareResult === DEEP_EQUAL) return {compareResult}
+
+    // Short-circut when values can be diffed directly.
+    if (
+      expected.tag === primitiveTag &&
+      this.value.tag === expected.value.tag && typeof this.value.diffDeep === 'function'
+    ) {
+      return {compareResult}
+    }
+
+    // Try to line up this or remaining items with the expected items.
+    const rhsFork = recursorUtils.fork(rhsRecursor)
+    const initialExpected = expected
+
+    do {
+      if (expected === null || expected.isItem !== true) {
+        return {
+          actualIsExtraneous: true,
+          rhsRecursor: recursorUtils.map(
+            recursorUtils.unshift(rhsFork.recursor, initialExpected),
+            next => {
+              if (next.isItem !== true) return next
+
+              next.index++
+              return next
+            })
+        }
+      }
+
+      if (this.value.compare(expected.value) === DEEP_EQUAL) {
+        return {
+          expectedIsMissing: true,
+          lhsRecursor: recursorUtils.map(
+            recursorUtils.unshift(lhsRecursor, this),
+            next => {
+              if (next.isItem !== true) return next
+
+              next.index++
+              return next
+            }),
+          rhsRecursor: rhsFork.recursor
+        }
+      }
+
+      expected = rhsFork.shared()
+    } while (true)
+  }
+
+  diffDeep (expected, theme, indent) {
+    // Verify a diff can be returned.
+    if (this.tag !== expected.tag || typeof this.value.diffDeep !== 'function') return null
+
+    const increaseValueIndent = theme.property.increaseValueIndent === true
+    const valueIndent = increaseValueIndent ? indent.increase() : indent
+
+    // Since the value is diffed directly, modifiers are not applied. Apply
+    // modifiers to the item descriptor instead.
+    const diff = this.value.diffDeep(expected.value, theme, valueIndent)
+    if (diff === null) return null
+
+    if (typeof theme.item.customFormat === 'function') {
+      return theme.item.customFormat(theme, indent, diff)
+    }
+
+    return diff.withLastPostfixed(theme.item.after)
+  }
+
+  serialize () {
+    return [this.index, this.value]
+  }
+}
+Object.defineProperty(PrimitiveItem.prototype, 'isItem', { value: true })
+Object.defineProperty(PrimitiveItem.prototype, 'tag', { value: primitiveTag })
diff --git a/node_modules/concordance/lib/metaDescriptors/mapEntry.js b/node_modules/concordance/lib/metaDescriptors/mapEntry.js
new file mode 100644
index 000000000..f1c100e4e
--- /dev/null
+++ b/node_modules/concordance/lib/metaDescriptors/mapEntry.js
@@ -0,0 +1,223 @@
+'use strict'
+
+const constants = require('../constants')
+const lineBuilder = require('../lineBuilder')
+const recursorUtils = require('../recursorUtils')
+const themeUtils = require('../themeUtils')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+
+function describe (keyDescriptor, valueDescriptor) {
+  const keyIsPrimitive = keyDescriptor.isPrimitive === true
+  const valueIsPrimitive = valueDescriptor.isPrimitive === true
+
+  return new MapEntry(keyDescriptor, valueDescriptor, keyIsPrimitive, valueIsPrimitive)
+}
+exports.describe = describe
+
+function deserialize (state, recursor) {
+  const keyIsPrimitive = state[0]
+  const valueIsPrimitive = state[1]
+  const keyDescriptor = recursor()
+  const valueDescriptor = recursor()
+
+  return new MapEntry(keyDescriptor, valueDescriptor, keyIsPrimitive, valueIsPrimitive)
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('MapEntry')
+exports.tag = tag
+
+function mergeWithKey (theme, key, values) {
+  const lines = lineBuilder.buffer()
+  const keyRemainder = lineBuilder.buffer()
+  for (const line of key) {
+    if (!line.isLast && !line.hasGutter) {
+      lines.append(line)
+    } else {
+      keyRemainder.append(line)
+    }
+  }
+  for (const value of values) {
+    lines.append(keyRemainder.mergeWithInfix(theme.mapEntry.separator, value).withLastPostfixed(theme.mapEntry.after))
+  }
+  return lines
+}
+
+class MapEntry {
+  constructor (key, value, keyIsPrimitive, valueIsPrimitive) {
+    this.key = key
+    this.value = value
+    this.keyIsPrimitive = keyIsPrimitive
+    this.valueIsPrimitive = valueIsPrimitive
+  }
+
+  createRecursor () {
+    let emitKey = true
+    let emitValue = true
+
+    return () => {
+      if (emitKey) {
+        emitKey = false
+        return this.key
+      }
+
+      if (emitValue) {
+        emitValue = false
+        return this.value
+      }
+
+      return null
+    }
+  }
+
+  compare (expected) {
+    if (this.tag !== expected.tag) return UNEQUAL
+    if (this.keyIsPrimitive !== expected.keyIsPrimitive) return UNEQUAL
+    if (this.valueIsPrimitive !== expected.valueIsPrimitive) return UNEQUAL
+
+    if (!this.keyIsPrimitive) return SHALLOW_EQUAL
+
+    const keyResult = this.key.compare(expected.key)
+    if (keyResult !== DEEP_EQUAL) return keyResult
+
+    if (!this.valueIsPrimitive) return SHALLOW_EQUAL
+    return this.value.compare(expected.value)
+  }
+
+  formatDeep (theme, indent) {
+    // Verify the map entry can be formatted directly.
+    if (!this.keyIsPrimitive || typeof this.value.formatDeep !== 'function') return null
+
+    // Since formatShallow() would result in theme modifiers being applied
+    // before the key and value are formatted, do the same here.
+    const value = this.value.formatDeep(themeUtils.applyModifiersToOriginal(this.value, theme), indent)
+    if (value === null) return null
+
+    const key = this.key.formatDeep(themeUtils.applyModifiersToOriginal(this.key, theme), indent)
+    return mergeWithKey(theme, key, [value])
+  }
+
+  formatShallow (theme, indent) {
+    let key = null
+    const values = []
+    return {
+      append: (formatted, origin) => {
+        if (this.key === origin) {
+          key = formatted
+        } else {
+          values.push(formatted)
+        }
+      },
+      finalize () {
+        return mergeWithKey(theme, key, values)
+      }
+    }
+  }
+
+  diffDeep (expected, theme, indent) {
+    // Verify a diff can be returned.
+    if (this.tag !== expected.tag || typeof this.value.diffDeep !== 'function') return null
+    // Only use this logic to format value diffs when the keys are primitive and equal.
+    if (!this.keyIsPrimitive || !expected.keyIsPrimitive || this.key.compare(expected.key) !== DEEP_EQUAL) {
+      return null
+    }
+
+    // Since formatShallow() would result in theme modifiers being applied
+    // before the key and value are formatted, do the same here.
+    const diff = this.value.diffDeep(expected.value, themeUtils.applyModifiersToOriginal(this.value, theme), indent)
+    if (diff === null) return null
+
+    const key = this.key.formatDeep(themeUtils.applyModifiersToOriginal(this.key, theme), indent, '')
+    return mergeWithKey(theme, key, [diff])
+  }
+
+  prepareDiff (expected, lhsRecursor, rhsRecursor, compareComplexShape, isCircular) {
+    // Circular values cannot be compared. They must be treated as being unequal when diffing.
+    if (isCircular(this.value) || isCircular(expected.value)) return {compareResult: UNEQUAL}
+
+    const compareResult = this.compare(expected)
+    const keysAreEqual = this.tag === expected.tag && this.key.compare(expected.key) === DEEP_EQUAL
+    // Short-circuit when keys and/or values are deeply equal.
+    if (compareResult === DEEP_EQUAL || keysAreEqual) return {compareResult}
+
+    // Try to line up this or remaining map entries with the expected entries.
+    const lhsFork = recursorUtils.fork(lhsRecursor)
+    const rhsFork = recursorUtils.fork(rhsRecursor)
+    const initialExpected = expected
+
+    let expectedIsMissing = false
+    while (!expectedIsMissing && expected !== null && this.tag === expected.tag) {
+      if (expected.keyIsPrimitive) {
+        expectedIsMissing = this.key.compare(expected.key) !== UNEQUAL
+      } else {
+        expectedIsMissing = compareComplexShape(this.key, expected.key) !== UNEQUAL
+      }
+
+      expected = rhsFork.shared()
+    }
+
+    let actualIsExtraneous = false
+    if (this.tag === initialExpected.tag) {
+      if (initialExpected.keyIsPrimitive) {
+        let actual = this
+        while (!actualIsExtraneous && actual !== null && this.tag === actual.tag) {
+          if (actual.keyIsPrimitive) {
+            actualIsExtraneous = initialExpected.key.compare(actual.key) === DEEP_EQUAL
+          }
+
+          actual = lhsFork.shared()
+        }
+      } else {
+        let actual = this
+        while (!actualIsExtraneous && actual !== null && this.tag === actual.tag) {
+          if (!actual.keyIsPrimitive) {
+            actualIsExtraneous = compareComplexShape(actual.key, initialExpected.key) !== UNEQUAL
+          }
+
+          actual = lhsFork.shared()
+        }
+      }
+    }
+
+    if (actualIsExtraneous && !expectedIsMissing) {
+      return {
+        actualIsExtraneous: true,
+        lhsRecursor: lhsFork.recursor,
+        rhsRecursor: recursorUtils.unshift(rhsFork.recursor, initialExpected)
+      }
+    }
+
+    if (expectedIsMissing && !actualIsExtraneous) {
+      return {
+        expectedIsMissing: true,
+        lhsRecursor: recursorUtils.unshift(lhsFork.recursor, this),
+        rhsRecursor: rhsFork.recursor
+      }
+    }
+
+    let mustRecurse = false
+    if (!this.keyIsPrimitive && !initialExpected.keyIsPrimitive) {
+      if (this.valueIsPrimitive || initialExpected.valueIsPrimitive) {
+        mustRecurse = this.value.compare(initialExpected.value) !== UNEQUAL
+      } else {
+        mustRecurse = compareComplexShape(this.value, initialExpected.value) !== UNEQUAL
+      }
+    }
+
+    return {
+      mustRecurse,
+      isUnequal: !mustRecurse,
+      lhsRecursor: lhsFork.recursor,
+      rhsRecursor: rhsFork.recursor
+    }
+  }
+
+  serialize () {
+    return [this.keyIsPrimitive, this.valueIsPrimitive]
+  }
+}
+Object.defineProperty(MapEntry.prototype, 'isMapEntry', { value: true })
+Object.defineProperty(MapEntry.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/metaDescriptors/pointer.js b/node_modules/concordance/lib/metaDescriptors/pointer.js
new file mode 100644
index 000000000..f569d2891
--- /dev/null
+++ b/node_modules/concordance/lib/metaDescriptors/pointer.js
@@ -0,0 +1,31 @@
+'use strict'
+
+const UNEQUAL = require('../constants').UNEQUAL
+
+function describe (index) {
+  return new Pointer(index)
+}
+exports.describe = describe
+
+exports.deserialize = describe
+
+const tag = Symbol('Pointer')
+exports.tag = tag
+
+class Pointer {
+  constructor (index) {
+    this.index = index
+  }
+
+  // Pointers cannot be compared, and are not expected to be part of the
+  // comparisons.
+  compare (expected) {
+    return UNEQUAL
+  }
+
+  serialize () {
+    return this.index
+  }
+}
+Object.defineProperty(Pointer.prototype, 'isPointer', { value: true })
+Object.defineProperty(Pointer.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/metaDescriptors/property.js b/node_modules/concordance/lib/metaDescriptors/property.js
new file mode 100644
index 000000000..b5d34271d
--- /dev/null
+++ b/node_modules/concordance/lib/metaDescriptors/property.js
@@ -0,0 +1,190 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const recursorUtils = require('../recursorUtils')
+const symbolPrimitive = require('../primitiveValues/symbol').tag
+
+const AMBIGUOUS = constants.AMBIGUOUS
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describeComplex (key, value) {
+  return new ComplexProperty(key, value)
+}
+exports.describeComplex = describeComplex
+
+function deserializeComplex (key, recursor) {
+  const value = recursor()
+  return new ComplexProperty(key, value)
+}
+exports.deserializeComplex = deserializeComplex
+
+function describePrimitive (key, value) {
+  return new PrimitiveProperty(key, value)
+}
+exports.describePrimitive = describePrimitive
+
+function deserializePrimitive (state) {
+  const key = state[0]
+  const value = state[1]
+  return new PrimitiveProperty(key, value)
+}
+exports.deserializePrimitive = deserializePrimitive
+
+const complexTag = Symbol('ComplexProperty')
+exports.complexTag = complexTag
+
+const primitiveTag = Symbol('PrimitiveProperty')
+exports.primitiveTag = primitiveTag
+
+class Property {
+  constructor (key) {
+    this.key = key
+  }
+
+  compareKeys (expected) {
+    const result = this.key.compare(expected.key)
+    // Return AMBIGUOUS if symbol keys are unequal. It's likely that properties
+    // are compared in order of declaration, which is not the desired strategy.
+    // Returning AMBIGUOUS allows compare() and diff() to recognize this
+    // situation and sort the symbol properties before comparing them.
+    return result === UNEQUAL && this.key.tag === symbolPrimitive && expected.key.tag === symbolPrimitive
+      ? AMBIGUOUS
+      : result
+  }
+
+  prepareDiff (expected, lhsRecursor, rhsRecursor, compareComplexShape, isCircular) {
+    // Circular values cannot be compared. They must be treated as being unequal when diffing.
+    if (isCircular(this.value) || isCircular(expected.value)) return {compareResult: UNEQUAL}
+
+    // Try to line up this or remaining properties with the expected properties.
+    const rhsFork = recursorUtils.fork(rhsRecursor)
+    const initialExpected = expected
+
+    do {
+      if (expected === null || expected.isProperty !== true) {
+        return {
+          actualIsExtraneous: true,
+          rhsRecursor: recursorUtils.unshift(rhsFork.recursor, initialExpected)
+        }
+      } else if (this.key.compare(expected.key) === DEEP_EQUAL) {
+        if (expected === initialExpected) {
+          return null
+        } else {
+          return {
+            expectedIsMissing: true,
+            lhsRecursor: recursorUtils.unshift(lhsRecursor, this),
+            rhsRecursor: rhsFork.recursor
+          }
+        }
+      }
+
+      expected = rhsFork.shared()
+    } while (true)
+  }
+}
+Object.defineProperty(Property.prototype, 'isProperty', { value: true })
+
+class ComplexProperty extends Property {
+  constructor (key, value) {
+    super(key)
+    this.value = value
+  }
+
+  createRecursor () {
+    return recursorUtils.singleValue(this.value)
+  }
+
+  compare (expected) {
+    if (expected.isProperty !== true) return UNEQUAL
+
+    const keyResult = this.compareKeys(expected)
+    if (keyResult !== DEEP_EQUAL) return keyResult
+
+    return this.tag === expected.tag
+      ? this.value.compare(expected.value)
+      : UNEQUAL
+  }
+
+  formatShallow (theme, indent) {
+    const increaseValueIndent = theme.property.increaseValueIndent === true
+    return new formatUtils.SingleValueFormatter(theme, value => {
+      if (typeof theme.property.customFormat === 'function') {
+        return theme.property.customFormat(theme, indent, this.key, value)
+      }
+
+      return value
+        .withFirstPrefixed(this.key.formatAsKey(theme) + theme.property.separator)
+        .withLastPostfixed(theme.property.after)
+    }, increaseValueIndent)
+  }
+
+  serialize () {
+    return this.key
+  }
+}
+Object.defineProperty(ComplexProperty.prototype, 'tag', { value: complexTag })
+
+class PrimitiveProperty extends Property {
+  constructor (key, value) {
+    super(key)
+    this.value = value
+  }
+
+  compare (expected) {
+    if (expected.isProperty !== true) return UNEQUAL
+
+    const keyResult = this.compareKeys(expected)
+    if (keyResult !== DEEP_EQUAL) return keyResult
+
+    return this.tag !== expected.tag
+      ? UNEQUAL
+      : this.value.compare(expected.value)
+  }
+
+  formatDeep (theme, indent) {
+    const increaseValueIndent = theme.property.increaseValueIndent === true
+    const valueIndent = increaseValueIndent ? indent.increase() : indent
+
+    // Since the key and value are formatted directly, modifiers are not
+    // applied. Apply modifiers to the property descriptor instead.
+    const formatted = this.value.formatDeep(theme, valueIndent)
+
+    if (typeof theme.property.customFormat === 'function') {
+      return theme.property.customFormat(theme, indent, this.key, formatted)
+    }
+
+    return formatted
+      .withFirstPrefixed(this.key.formatAsKey(theme) + theme.property.separator)
+      .withLastPostfixed(theme.property.after)
+  }
+
+  diffDeep (expected, theme, indent) {
+    // Verify a diff can be returned.
+    if (this.tag !== expected.tag || typeof this.value.diffDeep !== 'function') return null
+    // Only use this logic to diff values when the keys are the same.
+    if (this.key.compare(expected.key) !== DEEP_EQUAL) return null
+
+    const increaseValueIndent = theme.property.increaseValueIndent === true
+    const valueIndent = increaseValueIndent ? indent.increase() : indent
+
+    // Since the key and value are diffed directly, modifiers are not
+    // applied. Apply modifiers to the property descriptor instead.
+    const diff = this.value.diffDeep(expected.value, theme, valueIndent)
+    if (diff === null) return null
+
+    if (typeof theme.property.customFormat === 'function') {
+      return theme.property.customFormat(theme, indent, this.key, diff)
+    }
+
+    return diff
+      .withFirstPrefixed(this.key.formatAsKey(theme) + theme.property.separator)
+      .withLastPostfixed(theme.property.after)
+  }
+
+  serialize () {
+    return [this.key, this.value]
+  }
+}
+Object.defineProperty(PrimitiveProperty.prototype, 'tag', { value: primitiveTag })
diff --git a/node_modules/concordance/lib/metaDescriptors/stats.js b/node_modules/concordance/lib/metaDescriptors/stats.js
new file mode 100644
index 000000000..93bde9d1e
--- /dev/null
+++ b/node_modules/concordance/lib/metaDescriptors/stats.js
@@ -0,0 +1,136 @@
+'use strict'
+
+const constants = require('../constants')
+const lineBuilder = require('../lineBuilder')
+const recursorUtils = require('../recursorUtils')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describeIterableRecursor (recursor) {
+  return new IterableStats(recursor.size)
+}
+exports.describeIterableRecursor = describeIterableRecursor
+
+function describeListRecursor (recursor) {
+  return new ListStats(recursor.size)
+}
+exports.describeListRecursor = describeListRecursor
+
+function describePropertyRecursor (recursor) {
+  return new PropertyStats(recursor.size)
+}
+exports.describePropertyRecursor = describePropertyRecursor
+
+function deserializeIterableStats (size) {
+  return new IterableStats(size)
+}
+exports.deserializeIterableStats = deserializeIterableStats
+
+function deserializeListStats (size) {
+  return new ListStats(size)
+}
+exports.deserializeListStats = deserializeListStats
+
+function deserializePropertyStats (size) {
+  return new PropertyStats(size)
+}
+exports.deserializePropertyStats = deserializePropertyStats
+
+const iterableTag = Symbol('IterableStats')
+exports.iterableTag = iterableTag
+
+const listTag = Symbol('ListStats')
+exports.listTag = listTag
+
+const propertyTag = Symbol('PropertyStats')
+exports.propertyTag = propertyTag
+
+class Stats {
+  constructor (size) {
+    this.size = size
+  }
+
+  formatDeep (theme) {
+    return lineBuilder.single(theme.stats.separator)
+  }
+
+  prepareDiff (expected, lhsRecursor, rhsRecursor, compareComplexShape) {
+    if (expected.isStats !== true || expected.tag === this.tag) return null
+
+    // Try to line up stats descriptors with the same tag.
+    const rhsFork = recursorUtils.fork(rhsRecursor)
+    const initialExpected = expected
+
+    const missing = []
+    while (expected !== null && this.tag !== expected.tag) {
+      missing.push(expected)
+      expected = rhsFork.shared()
+    }
+
+    if (expected !== null && missing.length > 0) {
+      return {
+        multipleAreMissing: true,
+        descriptors: missing,
+        lhsRecursor: recursorUtils.unshift(lhsRecursor, this),
+        // Use original `rhsRecursor`, not `rhsFork`, since the consumed
+        // descriptors are returned with the `missing` array.
+        rhsRecursor: recursorUtils.unshift(rhsRecursor, expected)
+      }
+    }
+
+    const lhsFork = recursorUtils.fork(lhsRecursor)
+    let actual = this
+
+    const extraneous = []
+    while (actual !== null && actual.tag !== initialExpected.tag) {
+      extraneous.push(actual)
+      actual = lhsFork.shared()
+    }
+
+    if (actual !== null && extraneous.length > 0) {
+      return {
+        multipleAreExtraneous: true,
+        descriptors: extraneous,
+        // Use original `lhsRecursor`, not `lhsFork`, since the consumed
+        // descriptors are returned with the `extraneous` array.
+        lhsRecursor: recursorUtils.unshift(lhsRecursor, actual),
+        rhsRecursor: recursorUtils.unshift(rhsFork.recursor, initialExpected)
+      }
+    }
+
+    return null
+  }
+
+  serialize () {
+    return this.size
+  }
+}
+Object.defineProperty(Stats.prototype, 'isStats', { value: true })
+
+class IterableStats extends Stats {
+  compare (expected) {
+    return expected.tag === iterableTag && this.size === expected.size
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+}
+Object.defineProperty(IterableStats.prototype, 'tag', { value: iterableTag })
+
+class ListStats extends Stats {
+  compare (expected) {
+    return expected.tag === listTag && this.size === expected.size
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+}
+Object.defineProperty(ListStats.prototype, 'tag', { value: listTag })
+
+class PropertyStats extends Stats {
+  compare (expected) {
+    return expected.tag === propertyTag && this.size === expected.size
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+}
+Object.defineProperty(PropertyStats.prototype, 'tag', { value: propertyTag })
diff --git a/node_modules/concordance/lib/pluginRegistry.js b/node_modules/concordance/lib/pluginRegistry.js
new file mode 100644
index 000000000..b4fb76b37
--- /dev/null
+++ b/node_modules/concordance/lib/pluginRegistry.js
@@ -0,0 +1,222 @@
+'use strict'
+
+const semver = require('semver')
+
+const pkg = require('../package.json')
+const constants = require('./constants')
+const object = require('./complexValues/object')
+const lineBuilder = require('./lineBuilder')
+const formatUtils = require('./formatUtils')
+const itemDescriptor = require('./metaDescriptors/item')
+const propertyDescriptor = require('./metaDescriptors/property')
+const stringDescriptor = require('./primitiveValues/string')
+const recursorUtils = require('./recursorUtils')
+const themeUtils = require('./themeUtils')
+
+const API_VERSION = 1
+const CONCORDANCE_VERSION = pkg.version
+
+const descriptorRegistry = new Map()
+const registry = new Map()
+
+class PluginError extends Error {
+  constructor (message, plugin) {
+    super(message)
+    this.name = 'PluginError'
+    this.plugin = plugin
+  }
+}
+
+class PluginTypeError extends TypeError {
+  constructor (message, plugin) {
+    super(message)
+    this.name = 'PluginTypeError'
+    this.plugin = plugin
+  }
+}
+
+class UnsupportedApiError extends PluginError {
+  constructor (plugin) {
+    super('Plugin requires an unsupported API version', plugin)
+    this.name = 'UnsupportedApiError'
+  }
+}
+
+class UnsupportedError extends PluginError {
+  constructor (plugin) {
+    super('Plugin does not support this version of Concordance', plugin)
+    this.name = 'UnsupportedError'
+  }
+}
+
+class DuplicateDescriptorTagError extends PluginError {
+  constructor (tag, plugin) {
+    super(`Could not add descriptor: tag ${String(tag)} has already been registered`, plugin)
+    this.name = 'DuplicateDescriptorTagError'
+    this.tag = tag
+  }
+}
+
+class DuplicateDescriptorIdError extends PluginError {
+  constructor (id, plugin) {
+    const printed = typeof id === 'number'
+      ? `0x${id.toString(16).toUpperCase()}`
+      : String(id)
+    super(`Could not add descriptor: id ${printed} has already been registered`, plugin)
+    this.name = 'DuplicateDescriptorIdError'
+    this.id = id
+  }
+}
+
+function verify (plugin) {
+  if (typeof plugin.name !== 'string' || !plugin.name) {
+    throw new PluginTypeError('Plugin must have a `name`', plugin)
+  }
+
+  if (plugin.apiVersion !== API_VERSION) {
+    throw new UnsupportedApiError(plugin)
+  }
+
+  if ('minimalConcordanceVersion' in plugin) {
+    if (!semver.valid(plugin.minimalConcordanceVersion)) {
+      throw new PluginTypeError('If specified, `minimalConcordanceVersion` must be a valid SemVer version', plugin)
+    }
+
+    const range = `>=${plugin.minimalConcordanceVersion}`
+    if (!semver.satisfies(CONCORDANCE_VERSION, range)) {
+      throw new UnsupportedError(plugin)
+    }
+  }
+}
+
+// Selectively expose descriptor tags.
+const publicDescriptorTags = Object.freeze({
+  complexItem: itemDescriptor.complexTag,
+  primitiveItem: itemDescriptor.primitiveTag,
+  primitiveProperty: propertyDescriptor.primitiveTag,
+  string: stringDescriptor.tag
+})
+
+// Don't expose `setDefaultGutter()`.
+const publicLineBuilder = Object.freeze({
+  buffer: lineBuilder.buffer,
+  first: lineBuilder.first,
+  last: lineBuilder.last,
+  line: lineBuilder.line,
+  single: lineBuilder.single,
+  actual: Object.freeze({
+    buffer: lineBuilder.actual.buffer,
+    first: lineBuilder.actual.first,
+    last: lineBuilder.actual.last,
+    line: lineBuilder.actual.line,
+    single: lineBuilder.actual.single
+  }),
+  expected: Object.freeze({
+    buffer: lineBuilder.expected.buffer,
+    first: lineBuilder.expected.first,
+    last: lineBuilder.expected.last,
+    line: lineBuilder.expected.line,
+    single: lineBuilder.expected.single
+  })
+})
+
+function modifyTheme (descriptor, modifier) {
+  themeUtils.addModifier(descriptor, modifier)
+  return descriptor
+}
+
+function add (plugin) {
+  verify(plugin)
+
+  const name = plugin.name
+  if (registry.has(name)) return registry.get(name)
+
+  const id2deserialize = new Map()
+  const tag2id = new Map()
+  const addDescriptor = (id, tag, deserialize) => {
+    if (id2deserialize.has(id)) throw new DuplicateDescriptorIdError(id, plugin)
+    if (descriptorRegistry.has(tag) || tag2id.has(tag)) throw new DuplicateDescriptorTagError(tag, plugin)
+
+    id2deserialize.set(id, deserialize)
+    tag2id.set(tag, id)
+  }
+
+  const tryDescribeValue = plugin.register({
+    // Concordance makes assumptions about when AMBIGUOUS occurs. Do not expose
+    // it to plugins.
+    UNEQUAL: constants.UNEQUAL,
+    SHALLOW_EQUAL: constants.SHALLOW_EQUAL,
+    DEEP_EQUAL: constants.DEEP_EQUAL,
+
+    ObjectValue: object.ObjectValue,
+    DescribedMixin: object.DescribedMixin,
+    DeserializedMixin: object.DeserializedMixin,
+
+    addDescriptor,
+    applyThemeModifiers: themeUtils.applyModifiers,
+    descriptorTags: publicDescriptorTags,
+    lineBuilder: publicLineBuilder,
+    mapRecursor: recursorUtils.map,
+    modifyTheme,
+    wrapFromTheme: formatUtils.wrap
+  })
+
+  const registered = {
+    id2deserialize,
+    serializerVersion: plugin.serializerVersion,
+    name,
+    tag2id,
+    theme: plugin.theme || {},
+    tryDescribeValue
+  }
+
+  registry.set(name, registered)
+  for (const tag of tag2id.keys()) {
+    descriptorRegistry.set(tag, registered)
+  }
+
+  return registered
+}
+exports.add = add
+
+function getDeserializers (plugins) {
+  return plugins.map(plugin => {
+    const registered = add(plugin)
+    return {
+      id2deserialize: registered.id2deserialize,
+      name: registered.name,
+      serializerVersion: registered.serializerVersion
+    }
+  })
+}
+exports.getDeserializers = getDeserializers
+
+function getThemes (plugins) {
+  return plugins.map(plugin => {
+    const registered = add(plugin)
+    return {
+      name: registered.name,
+      theme: registered.theme
+    }
+  })
+}
+exports.getThemes = getThemes
+
+function getTryDescribeValues (plugins) {
+  return plugins.map(plugin => add(plugin).tryDescribeValue)
+}
+exports.getTryDescribeValues = getTryDescribeValues
+
+function resolveDescriptorRef (tag) {
+  if (!descriptorRegistry.has(tag)) return null
+
+  const registered = descriptorRegistry.get(tag)
+  return {
+    id: registered.tag2id.get(tag),
+    name: registered.name,
+    serialization: {
+      serializerVersion: registered.serializerVersion
+    }
+  }
+}
+exports.resolveDescriptorRef = resolveDescriptorRef
diff --git a/node_modules/concordance/lib/primitiveValues/boolean.js b/node_modules/concordance/lib/primitiveValues/boolean.js
new file mode 100644
index 000000000..7bad50408
--- /dev/null
+++ b/node_modules/concordance/lib/primitiveValues/boolean.js
@@ -0,0 +1,40 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (value) {
+  return new BooleanValue(value)
+}
+exports.describe = describe
+
+exports.deserialize = describe
+
+const tag = Symbol('BooleanValue')
+exports.tag = tag
+
+class BooleanValue {
+  constructor (value) {
+    this.value = value
+  }
+
+  compare (expected) {
+    return this.tag === expected.tag && this.value === expected.value
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatDeep (theme) {
+    return lineBuilder.single(formatUtils.wrap(theme.boolean, this.value === true ? 'true' : 'false'))
+  }
+
+  serialize () {
+    return this.value
+  }
+}
+Object.defineProperty(BooleanValue.prototype, 'isPrimitive', { value: true })
+Object.defineProperty(BooleanValue.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/primitiveValues/null.js b/node_modules/concordance/lib/primitiveValues/null.js
new file mode 100644
index 000000000..9436ed9a1
--- /dev/null
+++ b/node_modules/concordance/lib/primitiveValues/null.js
@@ -0,0 +1,32 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe () {
+  return new NullValue()
+}
+exports.describe = describe
+
+exports.deserialize = describe
+
+const tag = Symbol('NullValue')
+exports.tag = tag
+
+class NullValue {
+  compare (expected) {
+    return expected.tag === tag
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatDeep (theme) {
+    return lineBuilder.single(formatUtils.wrap(theme.null, 'null'))
+  }
+}
+Object.defineProperty(NullValue.prototype, 'isPrimitive', { value: true })
+Object.defineProperty(NullValue.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/primitiveValues/number.js b/node_modules/concordance/lib/primitiveValues/number.js
new file mode 100644
index 000000000..d1dec8edb
--- /dev/null
+++ b/node_modules/concordance/lib/primitiveValues/number.js
@@ -0,0 +1,41 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (value) {
+  return new NumberValue(value)
+}
+exports.describe = describe
+
+exports.deserialize = describe
+
+const tag = Symbol('NumberValue')
+exports.tag = tag
+
+class NumberValue {
+  constructor (value) {
+    this.value = value
+  }
+
+  compare (expected) {
+    return expected.tag === tag && Object.is(this.value, expected.value)
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatDeep (theme) {
+    const string = Object.is(this.value, -0) ? '-0' : String(this.value)
+    return lineBuilder.single(formatUtils.wrap(theme.number, string))
+  }
+
+  serialize () {
+    return this.value
+  }
+}
+Object.defineProperty(NumberValue.prototype, 'isPrimitive', { value: true })
+Object.defineProperty(NumberValue.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/primitiveValues/string.js b/node_modules/concordance/lib/primitiveValues/string.js
new file mode 100644
index 000000000..af120022f
--- /dev/null
+++ b/node_modules/concordance/lib/primitiveValues/string.js
@@ -0,0 +1,306 @@
+'use strict'
+
+const fastDiff = require('fast-diff')
+const keyword = require('esutils').keyword
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (value) {
+  return new StringValue(value)
+}
+exports.describe = describe
+
+exports.deserialize = describe
+
+const tag = Symbol('StringValue')
+exports.tag = tag
+
+// TODO: Escape invisible characters (e.g. zero-width joiner, non-breaking space),
+// ambiguous characters (other kinds of spaces, combining characters). Use
+// http://graphemica.com/blocks/control-pictures where applicable.
+function basicEscape (string) {
+  return string.replace(/\\/g, '\\\\')
+}
+
+const CRLF_CONTROL_PICTURE = '\u240D\u240A'
+const LF_CONTROL_PICTURE = '\u240A'
+const CR_CONTROL_PICTURE = '\u240D'
+
+const MATCH_CONTROL_PICTURES = new RegExp(`${CR_CONTROL_PICTURE}|${LF_CONTROL_PICTURE}|${CR_CONTROL_PICTURE}`, 'g')
+
+function escapeLinebreak (string) {
+  if (string === '\r\n') return CRLF_CONTROL_PICTURE
+  if (string === '\n') return LF_CONTROL_PICTURE
+  if (string === '\r') return CR_CONTROL_PICTURE
+  return string
+}
+
+function themeControlPictures (theme, resetWrap, str) {
+  return str.replace(MATCH_CONTROL_PICTURES, picture => {
+    return resetWrap.close + formatUtils.wrap(theme.string.controlPicture, picture) + resetWrap.open
+  })
+}
+
+const MATCH_SINGLE_QUOTE = /'/g
+const MATCH_DOUBLE_QUOTE = /"/g
+const MATCH_BACKTICKS = /`/g
+function escapeQuotes (line, string) {
+  const quote = line.escapeQuote
+  if (quote === '\'') return string.replace(MATCH_SINGLE_QUOTE, "\\'")
+  if (quote === '"') return string.replace(MATCH_DOUBLE_QUOTE, '\\"')
+  if (quote === '`') return string.replace(MATCH_BACKTICKS, '\\`')
+  return string
+}
+
+function includesLinebreaks (string) {
+  return string.includes('\r') || string.includes('\n')
+}
+
+function diffLine (theme, actual, expected) {
+  const outcome = fastDiff(actual, expected)
+
+  // TODO: Compute when line is mostly unequal (80%? 90%?) and treat it as being
+  // completely unequal.
+  const isPartiallyEqual = !(
+    (outcome.length === 2 && outcome[0][1] === actual && outcome[1][1] === expected) ||
+    // Discount line ending control pictures, which will be equal even when the
+    // rest of the line isn't.
+    (
+      outcome.length === 3 &&
+      outcome[2][0] === fastDiff.EQUAL &&
+      MATCH_CONTROL_PICTURES.test(outcome[2][1]) &&
+      outcome[0][1] + outcome[2][1] === actual &&
+      outcome[1][1] + outcome[2][1] === expected
+    )
+  )
+
+  let stringActual = ''
+  let stringExpected = ''
+
+  const noopWrap = { open: '', close: '' }
+  const deleteWrap = isPartiallyEqual ? theme.string.diff.delete : noopWrap
+  const insertWrap = isPartiallyEqual ? theme.string.diff.insert : noopWrap
+  const equalWrap = isPartiallyEqual ? theme.string.diff.equal : noopWrap
+  for (const diff of outcome) {
+    if (diff[0] === fastDiff.DELETE) {
+      stringActual += formatUtils.wrap(deleteWrap, diff[1])
+    } else if (diff[0] === fastDiff.INSERT) {
+      stringExpected += formatUtils.wrap(insertWrap, diff[1])
+    } else {
+      const string = formatUtils.wrap(equalWrap, themeControlPictures(theme, equalWrap, diff[1]))
+      stringActual += string
+      stringExpected += string
+    }
+  }
+
+  if (!isPartiallyEqual) {
+    stringActual = formatUtils.wrap(theme.string.diff.deleteLine, stringActual)
+    stringExpected = formatUtils.wrap(theme.string.diff.insertLine, stringExpected)
+  }
+
+  return [stringActual, stringExpected]
+}
+
+const LINEBREAKS = /\r\n|\r|\n/g
+
+function gatherLines (string) {
+  const lines = []
+  let prevIndex = 0
+  for (let match; (match = LINEBREAKS.exec(string)); prevIndex = match.index + match[0].length) {
+    lines.push(string.slice(prevIndex, match.index) + escapeLinebreak(match[0]))
+  }
+  lines.push(string.slice(prevIndex))
+  return lines
+}
+
+class StringValue {
+  constructor (value) {
+    this.value = value
+  }
+
+  compare (expected) {
+    return expected.tag === tag && this.value === expected.value
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  get includesLinebreaks () {
+    return includesLinebreaks(this.value)
+  }
+
+  formatDeep (theme, indent) {
+    // Escape backslashes
+    let escaped = basicEscape(this.value)
+
+    if (!this.includesLinebreaks) {
+      escaped = escapeQuotes(theme.string.line, escaped)
+      return lineBuilder.single(formatUtils.wrap(theme.string.line, formatUtils.wrap(theme.string, escaped)))
+    }
+
+    escaped = escapeQuotes(theme.string.multiline, escaped)
+    const lineStrings = gatherLines(escaped).map(string => {
+      return formatUtils.wrap(theme.string, themeControlPictures(theme, theme.string, string))
+    })
+    const lastIndex = lineStrings.length - 1
+    const indentation = indent
+    return lineBuilder.buffer()
+      .append(
+        lineStrings.map((string, index) => {
+          if (index === 0) return lineBuilder.first(theme.string.multiline.start + string)
+          if (index === lastIndex) return lineBuilder.last(indentation + string + theme.string.multiline.end)
+          return lineBuilder.line(indentation + string)
+        }))
+  }
+
+  formatAsKey (theme) {
+    const key = this.value
+    if (keyword.isIdentifierNameES6(key, true) || String(parseInt(key, 10)) === key) {
+      return key
+    }
+
+    const escaped = basicEscape(key)
+      .replace(/\n/g, '\\n')
+      .replace(/\r/g, '\\r')
+      .replace(/'/g, "\\'")
+    return formatUtils.wrap(theme.string.line, formatUtils.wrap(theme.string, escaped))
+  }
+
+  diffDeep (expected, theme, indent) {
+    if (expected.tag !== tag) return null
+
+    const escapedActual = basicEscape(this.value)
+    const escapedExpected = basicEscape(expected.value)
+
+    if (!includesLinebreaks(escapedActual) && !includesLinebreaks(escapedExpected)) {
+      const result = diffLine(theme,
+        escapeQuotes(theme.string.line, escapedActual),
+        escapeQuotes(theme.string.line, escapedExpected))
+
+      return lineBuilder.actual.single(formatUtils.wrap(theme.string.line, result[0]))
+        .concat(lineBuilder.expected.single(formatUtils.wrap(theme.string.line, result[1])))
+    }
+
+    const actualLines = gatherLines(escapeQuotes(theme.string.multiline, escapedActual))
+    const expectedLines = gatherLines(escapeQuotes(theme.string.multiline, escapedExpected))
+
+    const indentation = indent
+    const lines = lineBuilder.buffer()
+    const lastActualIndex = actualLines.length - 1
+    const lastExpectedIndex = expectedLines.length - 1
+
+    let actualBuffer = []
+    let expectedBuffer = []
+    let mustOpenNextExpected = false
+    for (let actualIndex = 0, expectedIndex = 0, extraneousOffset = 0; actualIndex < actualLines.length;) {
+      if (actualLines[actualIndex] === expectedLines[expectedIndex]) {
+        lines.append(actualBuffer)
+        lines.append(expectedBuffer)
+        actualBuffer = []
+        expectedBuffer = []
+
+        let string = actualLines[actualIndex]
+        string = themeControlPictures(theme, theme.string.diff.equal, string)
+        string = formatUtils.wrap(theme.string.diff.equal, string)
+
+        if (actualIndex === 0) {
+          lines.append(lineBuilder.first(theme.string.multiline.start + string))
+        } else if (actualIndex === lastActualIndex && expectedIndex === lastExpectedIndex) {
+          lines.append(lineBuilder.last(indentation + string + theme.string.multiline.end))
+        } else {
+          lines.append(lineBuilder.line(indentation + string))
+        }
+
+        actualIndex++
+        expectedIndex++
+        continue
+      }
+
+      let expectedIsMissing = false
+      {
+        const compare = actualLines[actualIndex]
+        for (let index = expectedIndex; !expectedIsMissing && index < expectedLines.length; index++) {
+          expectedIsMissing = compare === expectedLines[index]
+        }
+      }
+
+      let actualIsExtraneous = (actualIndex - extraneousOffset) > lastExpectedIndex
+      if (!actualIsExtraneous) {
+        const compare = expectedLines[expectedIndex]
+        for (let index = actualIndex; !actualIsExtraneous && index < actualLines.length; index++) {
+          actualIsExtraneous = compare === actualLines[index]
+        }
+
+        if (!actualIsExtraneous && (actualIndex - extraneousOffset) === lastExpectedIndex && actualIndex < lastActualIndex) {
+          actualIsExtraneous = true
+        }
+      }
+
+      if (actualIsExtraneous && !expectedIsMissing) {
+        const string = formatUtils.wrap(theme.string.diff.deleteLine, actualLines[actualIndex])
+
+        if (actualIndex === 0) {
+          actualBuffer.push(lineBuilder.actual.first(theme.string.multiline.start + string))
+          mustOpenNextExpected = true
+        } else if (actualIndex === lastActualIndex) {
+          actualBuffer.push(lineBuilder.actual.last(indentation + string + theme.string.multiline.end))
+        } else {
+          actualBuffer.push(lineBuilder.actual.line(indentation + string))
+        }
+
+        actualIndex++
+        extraneousOffset++
+      } else if (expectedIsMissing && !actualIsExtraneous) {
+        const string = formatUtils.wrap(theme.string.diff.insertLine, expectedLines[expectedIndex])
+
+        if (mustOpenNextExpected) {
+          expectedBuffer.push(lineBuilder.expected.first(theme.string.multiline.start + string))
+          mustOpenNextExpected = false
+        } else if (expectedIndex === lastExpectedIndex) {
+          expectedBuffer.push(lineBuilder.expected.last(indentation + string + theme.string.multiline.end))
+        } else {
+          expectedBuffer.push(lineBuilder.expected.line(indentation + string))
+        }
+
+        expectedIndex++
+      } else {
+        const result = diffLine(theme, actualLines[actualIndex], expectedLines[expectedIndex])
+
+        if (actualIndex === 0) {
+          actualBuffer.push(lineBuilder.actual.first(theme.string.multiline.start + result[0]))
+          mustOpenNextExpected = true
+        } else if (actualIndex === lastActualIndex) {
+          actualBuffer.push(lineBuilder.actual.last(indentation + result[0] + theme.string.multiline.end))
+        } else {
+          actualBuffer.push(lineBuilder.actual.line(indentation + result[0]))
+        }
+
+        if (mustOpenNextExpected) {
+          expectedBuffer.push(lineBuilder.expected.first(theme.string.multiline.start + result[1]))
+          mustOpenNextExpected = false
+        } else if (expectedIndex === lastExpectedIndex) {
+          expectedBuffer.push(lineBuilder.expected.last(indentation + result[1] + theme.string.multiline.end))
+        } else {
+          expectedBuffer.push(lineBuilder.expected.line(indentation + result[1]))
+        }
+
+        actualIndex++
+        expectedIndex++
+      }
+    }
+
+    lines.append(actualBuffer)
+    lines.append(expectedBuffer)
+    return lines
+  }
+
+  serialize () {
+    return this.value
+  }
+}
+Object.defineProperty(StringValue.prototype, 'isPrimitive', { value: true })
+Object.defineProperty(StringValue.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/primitiveValues/symbol.js b/node_modules/concordance/lib/primitiveValues/symbol.js
new file mode 100644
index 000000000..3778b4118
--- /dev/null
+++ b/node_modules/concordance/lib/primitiveValues/symbol.js
@@ -0,0 +1,114 @@
+'use strict'
+
+const stringEscape = require('js-string-escape')
+const wellKnownSymbols = require('well-known-symbols')
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe (value) {
+  let stringCompare = null
+
+  const key = Symbol.keyFor(value)
+  if (key !== undefined) {
+    stringCompare = `Symbol.for(${stringEscape(key)})`
+  } else if (wellKnownSymbols.isWellKnown(value)) {
+    stringCompare = wellKnownSymbols.getLabel(value)
+  }
+
+  return new SymbolValue({
+    stringCompare,
+    value
+  })
+}
+exports.describe = describe
+
+function deserialize (state) {
+  const stringCompare = state[0]
+  const string = state[1] || state[0]
+
+  return new DeserializedSymbolValue({
+    string,
+    stringCompare,
+    value: null
+  })
+}
+exports.deserialize = deserialize
+
+const tag = Symbol('SymbolValue')
+exports.tag = tag
+
+class SymbolValue {
+  constructor (props) {
+    this.stringCompare = props.stringCompare
+    this.value = props.value
+  }
+
+  compare (expected) {
+    if (expected.tag !== tag) return UNEQUAL
+
+    if (this.stringCompare !== null) {
+      return this.stringCompare === expected.stringCompare
+        ? DEEP_EQUAL
+        : UNEQUAL
+    }
+
+    return this.value === expected.value
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatString () {
+    if (this.stringCompare !== null) return this.stringCompare
+    return stringEscape(this.value.toString())
+  }
+
+  formatDeep (theme) {
+    return lineBuilder.single(formatUtils.wrap(theme.symbol, this.formatString()))
+  }
+
+  formatAsKey (theme) {
+    return formatUtils.wrap(theme.property.keyBracket, formatUtils.wrap(theme.symbol, this.formatString()))
+  }
+
+  serialize () {
+    const string = this.formatString()
+    return this.stringCompare === string
+      ? [this.stringCompare]
+      : [this.stringCompare, string]
+  }
+}
+Object.defineProperty(SymbolValue.prototype, 'isPrimitive', { value: true })
+Object.defineProperty(SymbolValue.prototype, 'tag', { value: tag })
+
+class DeserializedSymbolValue extends SymbolValue {
+  constructor (props) {
+    super(props)
+    this.string = props.string
+  }
+
+  compare (expected) {
+    if (expected.tag !== tag) return UNEQUAL
+
+    if (this.stringCompare !== null) {
+      return this.stringCompare === expected.stringCompare
+        ? DEEP_EQUAL
+        : UNEQUAL
+    }
+
+    // Symbols that are not in the global symbol registry, and are not
+    // well-known, cannot be compared when deserialized. Treat symbols
+    // as equal if they are formatted the same.
+    return this.string === expected.formatString()
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatString () {
+    return this.string
+  }
+}
diff --git a/node_modules/concordance/lib/primitiveValues/undefined.js b/node_modules/concordance/lib/primitiveValues/undefined.js
new file mode 100644
index 000000000..507556e61
--- /dev/null
+++ b/node_modules/concordance/lib/primitiveValues/undefined.js
@@ -0,0 +1,32 @@
+'use strict'
+
+const constants = require('../constants')
+const formatUtils = require('../formatUtils')
+const lineBuilder = require('../lineBuilder')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+function describe () {
+  return new UndefinedValue()
+}
+exports.describe = describe
+
+exports.deserialize = describe
+
+const tag = Symbol('UndefinedValue')
+exports.tag = tag
+
+class UndefinedValue {
+  compare (expected) {
+    return expected.tag === tag
+      ? DEEP_EQUAL
+      : UNEQUAL
+  }
+
+  formatDeep (theme) {
+    return lineBuilder.single(formatUtils.wrap(theme.undefined, 'undefined'))
+  }
+}
+Object.defineProperty(UndefinedValue.prototype, 'isPrimitive', { value: true })
+Object.defineProperty(UndefinedValue.prototype, 'tag', { value: tag })
diff --git a/node_modules/concordance/lib/recursorUtils.js b/node_modules/concordance/lib/recursorUtils.js
new file mode 100644
index 000000000..ff639b5b8
--- /dev/null
+++ b/node_modules/concordance/lib/recursorUtils.js
@@ -0,0 +1,110 @@
+'use strict'
+
+const NOOP_RECURSOR = {
+  size: 0,
+  next () { return null }
+}
+exports.NOOP_RECURSOR = NOOP_RECURSOR
+
+function fork (recursor) {
+  const buffer = []
+
+  return {
+    shared () {
+      const next = recursor()
+      if (next !== null) buffer.push(next)
+      return next
+    },
+
+    recursor () {
+      if (buffer.length > 0) return buffer.shift()
+      return recursor()
+    }
+  }
+}
+exports.fork = fork
+
+function map (recursor, mapFn) {
+  return () => {
+    const next = recursor()
+    if (next === null) return null
+
+    return mapFn(next)
+  }
+}
+exports.map = map
+
+function replay (state, create) {
+  if (!state) {
+    const recursor = create()
+    if (recursor === NOOP_RECURSOR) {
+      state = recursor
+    } else {
+      state = Object.assign({
+        buffer: [],
+        done: false
+      }, recursor)
+    }
+  }
+
+  if (state === NOOP_RECURSOR) return {state, recursor: state}
+
+  let done = false
+  let index = 0
+  const next = () => {
+    if (done) return null
+
+    let retval = state.buffer[index]
+    if (retval === undefined) {
+      retval = state.buffer[index] = state.next()
+    }
+
+    index++
+    if (retval === null) {
+      done = true
+    }
+    return retval
+  }
+
+  return {state, recursor: {next, size: state.size}}
+}
+exports.replay = replay
+
+function sequence (first, second) {
+  let fromFirst = true
+  return () => {
+    if (fromFirst) {
+      const next = first()
+      if (next !== null) return next
+
+      fromFirst = false
+    }
+
+    return second()
+  }
+}
+exports.sequence = sequence
+
+function singleValue (value) {
+  let done = false
+  return () => {
+    if (done) return null
+
+    done = true
+    return value
+  }
+}
+exports.singleValue = singleValue
+
+function unshift (recursor, value) {
+  return () => {
+    if (value !== null) {
+      const next = value
+      value = null
+      return next
+    }
+
+    return recursor()
+  }
+}
+exports.unshift = unshift
diff --git a/node_modules/concordance/lib/serialize.js b/node_modules/concordance/lib/serialize.js
new file mode 100644
index 000000000..07f568415
--- /dev/null
+++ b/node_modules/concordance/lib/serialize.js
@@ -0,0 +1,339 @@
+'use strict'
+
+const md5hex = require('md5-hex')
+
+const encoder = require('./encoder')
+const pluginRegistry = require('./pluginRegistry')
+
+const argumentsValue = require('./complexValues/arguments')
+const arrayBufferValue = require('./complexValues/arrayBuffer')
+const boxedValue = require('./complexValues/boxed')
+const dataViewValue = require('./complexValues/dataView')
+const dateValue = require('./complexValues/date')
+const errorValue = require('./complexValues/error')
+const functionValue = require('./complexValues/function')
+const globalValue = require('./complexValues/global')
+const mapValue = require('./complexValues/map')
+const objectValue = require('./complexValues/object')
+const promiseValue = require('./complexValues/promise')
+const regexpValue = require('./complexValues/regexp')
+const setValue = require('./complexValues/set')
+const typedArrayValue = require('./complexValues/typedArray')
+
+const itemDescriptor = require('./metaDescriptors/item')
+const mapEntryDescriptor = require('./metaDescriptors/mapEntry')
+const pointerDescriptor = require('./metaDescriptors/pointer')
+const propertyDescriptor = require('./metaDescriptors/property')
+const statsDescriptors = require('./metaDescriptors/stats')
+
+const booleanValue = require('./primitiveValues/boolean')
+const nullValue = require('./primitiveValues/null')
+const numberValue = require('./primitiveValues/number')
+const stringValue = require('./primitiveValues/string')
+const symbolValue = require('./primitiveValues/symbol')
+const undefinedValue = require('./primitiveValues/undefined')
+
+// Increment if encoding layout, descriptor IDs, or value types change. Previous
+// Concordance versions will not be able to decode buffers generated by a newer
+// version, so changing this value will require a major version bump of
+// Concordance itself. The version is encoded as an unsigned 16 bit integer.
+const VERSION = 2
+
+// Adding or removing mappings or changing an index requires the version in
+// encoder.js to be bumped, which necessitates a major version bump of
+// Concordance itself. Indexes are hexadecimal to make reading the binary
+// output easier.
+const mappings = [
+  [0x01, booleanValue.tag, booleanValue.deserialize],
+  [0x02, nullValue.tag, nullValue.deserialize],
+  [0x03, numberValue.tag, numberValue.deserialize],
+  [0x04, stringValue.tag, stringValue.deserialize],
+  [0x05, symbolValue.tag, symbolValue.deserialize],
+  [0x06, undefinedValue.tag, undefinedValue.deserialize],
+
+  [0x07, objectValue.tag, objectValue.deserialize],
+  [0x08, statsDescriptors.iterableTag, statsDescriptors.deserializeIterableStats],
+  [0x09, statsDescriptors.listTag, statsDescriptors.deserializeListStats],
+  [0x0A, itemDescriptor.complexTag, itemDescriptor.deserializeComplex],
+  [0x0B, itemDescriptor.primitiveTag, itemDescriptor.deserializePrimitive],
+  [0x0C, statsDescriptors.propertyTag, statsDescriptors.deserializePropertyStats],
+  [0x0D, propertyDescriptor.complexTag, propertyDescriptor.deserializeComplex],
+  [0x0E, propertyDescriptor.primitiveTag, propertyDescriptor.deserializePrimitive],
+  [0x0F, pointerDescriptor.tag, pointerDescriptor.deserialize],
+
+  [0x10, mapValue.tag, mapValue.deserialize],
+  [0x11, mapEntryDescriptor.tag, mapEntryDescriptor.deserialize],
+
+  [0x12, argumentsValue.tag, argumentsValue.deserialize],
+  [0x13, arrayBufferValue.tag, arrayBufferValue.deserialize],
+  [0x14, boxedValue.tag, boxedValue.deserialize],
+  [0x15, dataViewValue.tag, dataViewValue.deserialize],
+  [0x16, dateValue.tag, dateValue.deserialize],
+  [0x17, errorValue.tag, errorValue.deserialize],
+  [0x18, functionValue.tag, functionValue.deserialize],
+  [0x19, globalValue.tag, globalValue.deserialize],
+  [0x1A, promiseValue.tag, promiseValue.deserialize],
+  [0x1B, regexpValue.tag, regexpValue.deserialize],
+  [0x1C, setValue.tag, setValue.deserialize],
+  [0x1D, typedArrayValue.tag, typedArrayValue.deserialize],
+  [0x1E, typedArrayValue.bytesTag, typedArrayValue.deserializeBytes]
+]
+const tag2id = new Map(mappings.map(mapping => [mapping[1], mapping[0]]))
+const id2deserialize = new Map(mappings.map(mapping => [mapping[0], mapping[2]]))
+
+class DescriptorSerializationError extends Error {
+  constructor (descriptor) {
+    super('Could not serialize descriptor')
+    this.name = 'DescriptorSerializationError'
+    this.descriptor = descriptor
+  }
+}
+
+class MissingPluginError extends Error {
+  constructor (pluginName) {
+    super(`Could not deserialize buffer: missing plugin ${JSON.stringify(pluginName)}`)
+    this.name = 'MissingPluginError'
+    this.pluginName = pluginName
+  }
+}
+
+class PointerLookupError extends Error {
+  constructor (index) {
+    super(`Could not deserialize buffer: pointer ${index} could not be resolved`)
+    this.name = 'PointerLookupError'
+    this.index = index
+  }
+}
+
+class UnsupportedPluginError extends Error {
+  constructor (pluginName, serializerVersion) {
+    super(`Could not deserialize buffer: plugin ${JSON.stringify(pluginName)} expects a different serialization`)
+    this.name = 'UnsupportedPluginError'
+    this.pluginName = pluginName
+    this.serializerVersion = serializerVersion
+  }
+}
+
+class UnsupportedVersion extends Error {
+  constructor (serializerVersion) {
+    super('Could not deserialize buffer: a different serialization was expected')
+    this.name = 'UnsupportedVersion'
+    this.serializerVersion = serializerVersion
+  }
+}
+
+function shallowSerializeDescriptor (descriptor, resolvePluginRef) {
+  if (!descriptor.serialize) return undefined
+
+  return serializeState(descriptor.serialize(), resolvePluginRef)
+}
+
+function serializeState (state, resolvePluginRef) {
+  if (Array.isArray(state)) return state.map(serializeState)
+
+  if (state && state.tag) {
+    let id, pluginIndex
+    if (tag2id.has(state.tag)) {
+      id = tag2id.get(state.tag)
+      pluginIndex = 0
+    } else {
+      const ref = resolvePluginRef(state.tag)
+      if (ref) {
+        id = ref.id
+        pluginIndex = ref.pluginIndex
+      }
+    }
+
+    if (id !== undefined) {
+      const serialized = [pluginIndex, id, shallowSerializeDescriptor(state, resolvePluginRef)]
+      serialized[encoder.descriptorSymbol] = true
+      return serialized
+    }
+  }
+
+  return state
+}
+
+function serialize (descriptor) {
+  const usedPlugins = new Map()
+  const resolvePluginRef = tag => {
+    const ref = pluginRegistry.resolveDescriptorRef(tag)
+    if (!ref) return null
+
+    if (!usedPlugins.has(ref.name)) {
+      // Start at 1, since 0 is reserved for Concordance's descriptors.
+      const index = usedPlugins.size + 1
+      usedPlugins.set(ref.name, Object.assign({index}, ref.serialization))
+    }
+
+    return {
+      id: ref.id,
+      pluginIndex: usedPlugins.get(ref.name).index
+    }
+  }
+
+  const seen = new Set()
+
+  const stack = []
+  let topIndex = -1
+
+  let rootRecord
+  do {
+    if (descriptor.isComplex === true) {
+      if (seen.has(descriptor.pointer)) {
+        descriptor = pointerDescriptor.describe(descriptor.pointer)
+      } else {
+        seen.add(descriptor.pointer)
+      }
+    }
+
+    let id
+    let pluginIndex = 0
+    if (tag2id.has(descriptor.tag)) {
+      id = tag2id.get(descriptor.tag)
+    } else {
+      const ref = resolvePluginRef(descriptor.tag)
+      if (!ref) throw new DescriptorSerializationError(descriptor)
+
+      id = ref.id
+      pluginIndex = ref.pluginIndex
+    }
+
+    const record = {
+      id,
+      pluginIndex,
+      children: [],
+      state: shallowSerializeDescriptor(descriptor, resolvePluginRef)
+    }
+    if (!rootRecord) {
+      rootRecord = record
+    } else {
+      stack[topIndex].children.push(record)
+    }
+
+    if (descriptor.createRecursor) {
+      stack.push({ recursor: descriptor.createRecursor(), children: record.children })
+      topIndex++
+    }
+
+    while (topIndex >= 0) {
+      descriptor = stack[topIndex].recursor()
+      if (descriptor === null) {
+        stack.pop()
+        topIndex--
+      } else {
+        break
+      }
+    }
+  } while (topIndex >= 0)
+
+  return encoder.encode(VERSION, rootRecord, usedPlugins)
+}
+exports.serialize = serialize
+
+function deserializeState (state, getDescriptorDeserializer) {
+  if (state && state[encoder.descriptorSymbol] === true) {
+    return shallowDeserializeDescriptor(state, getDescriptorDeserializer)
+  }
+
+  return Array.isArray(state)
+    ? state.map(item => deserializeState(item, getDescriptorDeserializer))
+    : state
+}
+
+function shallowDeserializeDescriptor (entry, getDescriptorDeserializer) {
+  const deserializeDescriptor = getDescriptorDeserializer(entry[0], entry[1])
+  return deserializeDescriptor(entry[2])
+}
+
+function deserializeRecord (record, getDescriptorDeserializer, buffer) {
+  const deserializeDescriptor = getDescriptorDeserializer(record.pluginIndex, record.id)
+  const state = deserializeState(record.state, getDescriptorDeserializer)
+
+  if (record.pointerAddresses.length === 0) {
+    return deserializeDescriptor(state)
+  }
+
+  const endIndex = record.pointerAddresses.length
+  let index = 0
+  const recursor = () => {
+    if (index === endIndex) return null
+
+    const recursorRecord = encoder.decodeRecord(buffer, record.pointerAddresses[index++])
+    return deserializeRecord(recursorRecord, getDescriptorDeserializer, buffer)
+  }
+
+  return deserializeDescriptor(state, recursor)
+}
+
+function buildPluginMap (buffer, options) {
+  const cache = options && options.deserializedPluginsCache
+  const cacheKey = md5hex(buffer)
+  if (cache && cache.has(cacheKey)) return cache.get(cacheKey)
+
+  const decodedPlugins = encoder.decodePlugins(buffer)
+  if (decodedPlugins.size === 0) {
+    const pluginMap = new Map()
+    if (cache) cache.set(cacheKey, pluginMap)
+    return pluginMap
+  }
+
+  const deserializerLookup = new Map()
+  if (Array.isArray(options && options.plugins)) {
+    for (const deserializer of pluginRegistry.getDeserializers(options.plugins)) {
+      deserializerLookup.set(deserializer.name, deserializer)
+    }
+  }
+
+  const pluginMap = new Map()
+  for (const index of decodedPlugins.keys()) {
+    const used = decodedPlugins.get(index)
+    const pluginName = used.name
+    const serializerVersion = used.serializerVersion
+
+    // TODO: Allow plugin author to encode a helpful message in its serialization
+    if (!deserializerLookup.has(pluginName)) {
+      throw new MissingPluginError(pluginName)
+    }
+    if (serializerVersion !== deserializerLookup.get(pluginName).serializerVersion) {
+      throw new UnsupportedPluginError(pluginName, serializerVersion)
+    }
+
+    pluginMap.set(index, deserializerLookup.get(pluginName).id2deserialize)
+  }
+
+  if (cache) cache.set(cacheKey, pluginMap)
+  return pluginMap
+}
+
+function deserialize (buffer, options) {
+  const version = encoder.extractVersion(buffer)
+  if (version !== VERSION) throw new UnsupportedVersion(version)
+
+  const decoded = encoder.decode(buffer)
+  const pluginMap = buildPluginMap(decoded.pluginBuffer, options)
+
+  const descriptorsByPointerIndex = new Map()
+  const mapPointerDescriptor = descriptor => {
+    if (descriptor.isPointer === true) {
+      if (!descriptorsByPointerIndex.has(descriptor.index)) throw new PointerLookupError(descriptor.index)
+
+      return descriptorsByPointerIndex.get(descriptor.index)
+    } else if (descriptor.isComplex === true) {
+      descriptorsByPointerIndex.set(descriptor.pointer, descriptor)
+    }
+    return descriptor
+  }
+
+  const getDescriptorDeserializer = (pluginIndex, id) => {
+    return (state, recursor) => {
+      const deserializeDescriptor = pluginIndex === 0
+        ? id2deserialize.get(id)
+        : pluginMap.get(pluginIndex).get(id)
+
+      return mapPointerDescriptor(deserializeDescriptor(state, recursor))
+    }
+  }
+  return deserializeRecord(decoded.rootRecord, getDescriptorDeserializer, buffer)
+}
+exports.deserialize = deserialize
diff --git a/node_modules/concordance/lib/shouldCompareDeep.js b/node_modules/concordance/lib/shouldCompareDeep.js
new file mode 100644
index 000000000..a59135507
--- /dev/null
+++ b/node_modules/concordance/lib/shouldCompareDeep.js
@@ -0,0 +1,17 @@
+'use strict'
+
+const argumentsObject = require('./complexValues/arguments').tag
+const constants = require('./constants')
+
+const AMBIGUOUS = constants.AMBIGUOUS
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+
+function shouldCompareDeep (result, lhs, rhs) {
+  if (result === SHALLOW_EQUAL) return true
+  if (result !== AMBIGUOUS) return false
+
+  // Properties are only ambiguous if they have symbol keys. These properties
+  // must be compared in an order-insensitive manner.
+  return lhs.tag === argumentsObject || lhs.isProperty === true
+}
+module.exports = shouldCompareDeep
diff --git a/node_modules/concordance/lib/symbolProperties.js b/node_modules/concordance/lib/symbolProperties.js
new file mode 100644
index 000000000..623a428fc
--- /dev/null
+++ b/node_modules/concordance/lib/symbolProperties.js
@@ -0,0 +1,106 @@
+'use strict'
+
+const constants = require('./constants')
+const recursorUtils = require('./recursorUtils')
+
+const DEEP_EQUAL = constants.DEEP_EQUAL
+const SHALLOW_EQUAL = constants.SHALLOW_EQUAL
+const UNEQUAL = constants.UNEQUAL
+
+class Comparable {
+  constructor (properties) {
+    this.properties = properties
+    this.ordered = properties.slice()
+  }
+
+  createRecursor () {
+    const length = this.ordered.length
+    let index = 0
+    return () => {
+      if (index === length) return null
+
+      return this.ordered[index++]
+    }
+  }
+
+  compare (expected) {
+    if (this.properties.length !== expected.properties.length) return UNEQUAL
+
+    // Compare property keys, reordering the expected properties in the process
+    // so values can be compared if all keys are equal.
+    const ordered = []
+    const processed = new Set()
+    for (const property of this.properties) {
+      let extraneous = true
+      for (const other of expected.properties) {
+        if (processed.has(other.key)) continue
+
+        if (property.key.compare(other.key) === DEEP_EQUAL) {
+          extraneous = false
+          processed.add(other.key)
+          ordered.push(other)
+          break
+        }
+      }
+
+      if (extraneous) return UNEQUAL
+    }
+    expected.ordered = ordered
+
+    return SHALLOW_EQUAL
+  }
+
+  prepareDiff (expected) {
+    // Reorder the expected properties before recursion starts.
+    const missingProperties = []
+    const ordered = []
+    const processed = new Set()
+    for (const other of expected.properties) {
+      let missing = true
+      for (const property of this.properties) {
+        if (processed.has(property.key)) continue
+
+        if (property.key.compare(other.key) === DEEP_EQUAL) {
+          missing = false
+          processed.add(property.key)
+          ordered.push(other)
+          break
+        }
+      }
+
+      if (missing) {
+        missingProperties.push(other)
+      }
+    }
+    expected.ordered = ordered.concat(missingProperties)
+
+    return {mustRecurse: true}
+  }
+}
+Object.defineProperty(Comparable.prototype, 'isSymbolPropertiesComparable', { value: true })
+exports.Comparable = Comparable
+
+class Collector {
+  constructor (firstProperty, recursor) {
+    this.properties = [firstProperty]
+    this.recursor = recursor
+    this.remainder = null
+  }
+
+  collectAll () {
+    do {
+      const next = this.recursor()
+      if (next && next.isProperty === true) { // All properties will have symbol keys
+        this.properties.push(next)
+      } else {
+        return next
+      }
+    } while (true)
+  }
+
+  createRecursor () {
+    return recursorUtils.singleValue(new Comparable(this.properties))
+  }
+}
+Object.defineProperty(Collector.prototype, 'isSymbolPropertiesCollector', { value: true })
+exports.Collector = Collector
diff --git a/node_modules/concordance/lib/themeUtils.js b/node_modules/concordance/lib/themeUtils.js
new file mode 100644
index 000000000..a0a64b586
--- /dev/null
+++ b/node_modules/concordance/lib/themeUtils.js
@@ -0,0 +1,195 @@
+'use strict'
+
+const cloneDeep = require('lodash.clonedeep')
+const merge = require('lodash.merge')
+
+const pluginRegistry = require('./pluginRegistry')
+
+function freezeTheme (theme) {
+  const queue = [theme]
+  while (queue.length > 0) {
+    const object = queue.shift()
+    Object.freeze(object)
+
+    for (const key of Object.keys(object)) {
+      const value = object[key]
+      if (value !== null && typeof value === 'object') {
+        queue.push(value)
+      }
+    }
+  }
+
+  return theme
+}
+
+const defaultTheme = freezeTheme({
+  boolean: { open: '', close: '' },
+  circular: '[Circular]',
+  date: {
+    invalid: 'invalid',
+    value: { open: '', close: '' }
+  },
+  diffGutters: {
+    actual: '- ',
+    expected: '+ ',
+    padding: '  '
+  },
+  error: {
+    ctor: { open: '(', close: ')' },
+    name: { open: '', close: '' }
+  },
+  function: {
+    name: { open: '', close: '' },
+    stringTag: { open: '', close: '' }
+  },
+  global: { open: '', close: '' },
+  item: {
+    after: ',',
+    customFormat: null,
+    increaseValueIndent: false
+  },
+  list: { openBracket: '[', closeBracket: ']' },
+  mapEntry: {
+    after: ',',
+    separator: ' => '
+  },
+  maxDepth: '…',
+  null: { open: '', close: '' },
+  number: { open: '', close: '' },
+  object: {
+    openBracket: '{',
+    closeBracket: '}',
+    ctor: { open: '', close: '' },
+    stringTag: { open: '@', close: '' },
+    secondaryStringTag: { open: '@', close: '' }
+  },
+  property: {
+    after: ',',
+    customFormat: null,
+    keyBracket: { open: '[', close: ']' },
+    separator: ': ',
+    increaseValueIndent: false
+  },
+  regexp: {
+    source: { open: '/', close: '/' },
+    flags: { open: '', close: '' },
+    separator: '---'
+  },
+  stats: { separator: '---' },
+  string: {
+    open: '',
+    close: '',
+    line: { open: "'", close: "'", escapeQuote: "'" },
+    multiline: { start: '`', end: '`', escapeQuote: '``' },
+    controlPicture: { open: '', close: '' },
+    diff: {
+      insert: { open: '', close: '' },
+      delete: { open: '', close: '' },
+      equal: { open: '', close: '' },
+      insertLine: { open: '', close: '' },
+      deleteLine: { open: '', close: '' }
+    }
+  },
+  symbol: { open: '', close: '' },
+  typedArray: {
+    bytes: { open: '', close: '' }
+  },
+  undefined: { open: '', close: '' }
+})
+
+const pluginRefs = new Map()
+pluginRefs.count = 0
+const normalizedPluginThemes = new Map()
+function normalizePlugins (plugins) {
+  if (!Array.isArray(plugins) || plugins.length === 0) return null
+
+  const refs = []
+  const themes = []
+  for (const fromPlugin of pluginRegistry.getThemes(plugins)) {
+    if (!pluginRefs.has(fromPlugin.name)) {
+      pluginRefs.set(fromPlugin.name, pluginRefs.count++)
+    }
+
+    refs.push(pluginRefs.get(fromPlugin.name))
+    themes.push(fromPlugin.theme)
+  }
+
+  const ref = refs.join('.')
+  if (normalizedPluginThemes.has(ref)) {
+    return {
+      ref,
+      theme: normalizedPluginThemes.get(ref)
+    }
+  }
+
+  const theme = freezeTheme(themes.reduce((acc, pluginTheme) => {
+    return merge(acc, pluginTheme)
+  }, cloneDeep(defaultTheme)))
+  normalizedPluginThemes.set(ref, theme)
+  return {ref, theme}
+}
+
+const normalizedCache = new WeakMap()
+function normalize (options) {
+  options = Object.assign({plugins: [], theme: null}, options)
+
+  const normalizedPlugins = normalizePlugins(options.plugins)
+  if (!options.theme) {
+    return normalizedPlugins ? normalizedPlugins.theme : defaultTheme
+  }
+
+  const entry = normalizedCache.get(options.theme) || {theme: null, withPlugins: new Map()}
+  if (!normalizedCache.has(options.theme)) normalizedCache.set(options.theme, entry)
+
+  if (normalizedPlugins) {
+    if (entry.withPlugins.has(normalizedPlugins.ref)) {
+      return entry.withPlugins.get(normalizedPlugins.ref)
+    }
+
+    const theme = freezeTheme(merge(cloneDeep(normalizedPlugins.theme), options.theme))
+    entry.withPlugins.set(normalizedPlugins.ref, theme)
+    return theme
+  }
+
+  if (!entry.theme) {
+    entry.theme = freezeTheme(merge(cloneDeep(defaultTheme), options.theme))
+  }
+  return entry.theme
+}
+exports.normalize = normalize
+
+const modifiers = new WeakMap()
+function addModifier (descriptor, modifier) {
+  if (modifiers.has(descriptor)) {
+    modifiers.get(descriptor).add(modifier)
+  } else {
+    modifiers.set(descriptor, new Set([modifier]))
+  }
+}
+exports.addModifier = addModifier
+
+const modifierCache = new WeakMap()
+const originalCache = new WeakMap()
+function applyModifiers (descriptor, theme) {
+  if (!modifiers.has(descriptor)) return theme
+
+  return Array.from(modifiers.get(descriptor)).reduce((prev, modifier) => {
+    const cache = modifierCache.get(modifier) || new WeakMap()
+    if (!modifierCache.has(modifier)) modifierCache.set(modifier, cache)
+
+    if (cache.has(prev)) return cache.get(prev)
+
+    const modifiedTheme = cloneDeep(prev)
+    modifier(modifiedTheme)
+    freezeTheme(modifiedTheme)
+    cache.set(prev, modifiedTheme)
+    originalCache.set(modifiedTheme, theme)
+    return modifiedTheme
+  }, theme)
+}
+exports.applyModifiers = applyModifiers
+
+function applyModifiersToOriginal (descriptor, theme) {
+  return applyModifiers(descriptor, originalCache.get(theme) || theme)
+}
+exports.applyModifiersToOriginal = applyModifiersToOriginal