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+<pre>
+  BIP: 386
+  Layer: Applications
+  Title: tr() Output Script Descriptors
+  Author: Pieter Wuille <pieter@wuille.net>
+          Ava Chow <me@achow101.com>
+  Comments-Summary: No comments yet.
+  Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0386
+  Status: Draft
+  Type: Informational
+  Created: 2021-06-27
+  License: BSD-2-Clause
+</pre>
+
+==Abstract==
+
+This document specifies <tt>tr()</tt> output script descriptors.
+<tt>tr()</tt> descriptors take a key and optionally a tree of scripts and produces a P2TR output script.
+
+==Copyright==
+
+This BIP is licensed under the BSD 2-clause license.
+
+==Motivation==
+
+Taproot added one additional standard output script format: P2TR.
+These expressions allow specifying those formats as a descriptor.
+
+==Specification==
+
+A new script expression is defined: <tt>tr()</tt>.
+A new expression is defined: Tree Expressions
+
+===Tree Expression===
+
+A Tree Expression (denoted <tt>TREE</tt>) is an expression which represents a tree of scripts.
+The way the tree is represented in an output script is dependent on the higher level expressions.
+
+A Tree Expression is:
+* Any Script Expression that is allowed at the level this Tree Expression is in.
+* A pair of Tree Expressions consisting of:
+** An open brace <tt>{</tt>
+** A Tree Expression
+** A comma <tt>,</tt>
+** A Tree Expression
+** A closing brace <tt>}</tt>
+
+===<tt>tr()</tt>===
+
+The <tt>tr(KEY)</tt> or <tt>tr(KEY, TREE)</tt> expression can only be used as a top level expression.
+All key expressions under any <tt>tr()</tt> expression must create x-only public keys.
+
+<tt>tr(KEY)</tt> takes a single key expression as an argument and produces a P2TR output script which does not have a script path.
+Each key produced by the key expression is used as the internal key of a P2TR output as specified by [[bip-0341.mediawiki#cite_ref-22-0|BIP 341]].
+Specifically, "If the spending conditions do not require a script path, the output key should commit to an unspendable script path instead of having no script path.
+This can be achieved by computing the output key point as ''Q = P + int(hash<sub>TapTweak</sub>(bytes(P)))G''."
+
+<pre>
+internal_key:       lift_x(KEY)
+32_byte_output_key: internal_key + int(HashTapTweak(bytes(internal_key)))G
+scriptPubKey:       OP_1 <32_byte_output_key>
+</pre>
+
+<tt>tr(KEY, TREE)</tt> takes a key expression as the first argument, and a tree expression as the second argument and produces a P2TR output script which has a script path.
+The keys produced by the first key expression are used as the internal key as specified by [[bip-0341.mediawiki#Constructing_and_spending_Taproot_outputs|BIP 341]].
+The Tree expression becomes the Taproot script tree as described in BIP 341.
+A merkle root is computed from this tree and combined with the internal key to create the Taproot output key.
+
+<pre>
+internal_key:       lift_x(KEY)
+merkle_root:        HashTapBranch(TREE)
+32_byte_output_key: internal_key + int(HashTapTweak(bytes(internal_key) || merkle_root))G
+scriptPubKey:       OP_1 <32_byte_output_key>
+</pre>
+
+===Modified Key Expression===
+
+Key Expressions within a <tt>tr()</tt> expression must only create x-only public keys.
+Uncompressed public keys are not allowed, but compressed public keys would be implicitly converted to x-only public keys.
+The keys derived from extended keys must be serialized as x-only public keys.
+An additional key expression is defined only for use within a <tt>tr()</tt> descriptor:
+
+* A 64 hex character string representing an x-only public key
+
+==Test Vectors==
+
+Valid descriptors followed by the scripts they produce. Descriptors involving derived child keys will have the 0th, 1st, and 2nd scripts listed.
+
+* <tt>tr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd)</tt>
+** <tt>512077aab6e066f8a7419c5ab714c12c67d25007ed55a43cadcacb4d7a970a093f11</tt>
+* <tt>tr(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1)</tt>
+** <tt>512077aab6e066f8a7419c5ab714c12c67d25007ed55a43cadcacb4d7a970a093f11</tt>
+* <tt>tr(xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/0/*,pk(xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc/1/*))</tt>
+** <tt>512078bc707124daa551b65af74de2ec128b7525e10f374dc67b64e00ce0ab8b3e12</tt>
+** <tt>512001f0a02a17808c20134b78faab80ef93ffba82261ccef0a2314f5d62b6438f11</tt>
+** <tt>512021024954fcec88237a9386fce80ef2ced5f1e91b422b26c59ccfc174c8d1ad25</tt>
+* <tt>tr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd,pk(669b8afcec803a0d323e9a17f3ea8e68e8abe5a278020a929adbec52421adbd0))</tt>
+** <tt>512017cf18db381d836d8923b1bdb246cfcd818da1a9f0e6e7907f187f0b2f937754</tt>
+* <tt>tr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd,{pk(xprvA2JDeKCSNNZky6uBCviVfJSKyQ1mDYahRjijr5idH2WwLsEd4Hsb2Tyh8RfQMuPh7f7RtyzTtdrbdqqsunu5Mm3wDvUAKRHSC34sJ7in334/0),{{pk(xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL),pk(02df12b7035bdac8e3bab862a3a83d06ea6b17b6753d52edecba9be46f5d09e076)},pk(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1)}})</tt>
+** <tt>512071fff39599a7b78bc02623cbe814efebf1a404f5d8ad34ea80f213bd8943f574</tt>
+
+Invalid Descriptors
+
+* Uncompressed private key: <tt>tr(5kyzdueo39z3fprtux2qbbwgnnp5ztd7yyr2sc1j299sbcnwjss)</tt>
+* Uncompressed public key: <tt>tr(04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235)</tt>
+* <tt>tr()</tt> nested in <tt>wsh</tt>: <tt>wsh(tr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))</tt>
+* <tt>tr()</tt> nested in <tt>sh</tt>: <tt>sh(tr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))</tt>
+* <tt>pkh()</tt> nested in <tt>tr</tt>: <tt>tr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd, pkh(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1))</tt>
+
+==Backwards Compatibility==
+
+<tt>tr()</tt> descriptors use the format and general operation specified in [[bip-0380.mediawiki|380]].
+As these are a set of wholly new descriptors, they are not compatible with any implementation.
+However the scripts produced are standard scripts so existing software are likely to be familiar with them.
+
+Tree Expressions are largely incompatible with existing script expressions due to the restrictions in those expressions.
+As of 2021-06-27, the only allowed script expression that can be used in a tree expression is <tt>pk()</tt>.
+However there will be future BIPs that specify script expressions that can be used in tree expressions.
+
+==Reference Implementation==
+
+<tt>tr()</tt> descriptors have been implemented in Bitcoin Core since version 22.0.