[doc] remove non-signaling mentions of BIP125

Our RBF policy is different from the rules specified in BIP125. For
example, the BIP does not mention Rule 6, and our Rule 4 uses the
(configurable) incremental relay feerate (distinct from the
minimum relay feerate). Those interested in our policy should refer to
doc/policy/mempool-replacements.md instead. These rules may also
continue to diverge with package RBF and other RBF improvements. Keep
references to the BIP125 signaling wrt sequence numbers, since that is
still correct and widely used. It is helpful to refer to this as "BIP125
signaling" since it is unambiguous and succint, especially if we have
multiple ways to signal replaceability in the future.

The rule numbers in doc/policy/mempool-replacements.md correspond
largely to those of BIP 125, so we can still refer to them like "Rule 5."

3 files changed, 19 insertions, 19 deletions

diff --git a/src/policy/policy.h b/src/policy/policy.h
index 3d2660b081..29764ea2d9 100644
--- a/src/policy/policy.h
+++ b/src/policy/policy.h
@@ -31,7 +31,7 @@ static constexpr unsigned int MIN_STANDARD_TX_NONWITNESS_SIZE{82};
 static constexpr unsigned int MAX_P2SH_SIGOPS{15};
 /** The maximum number of sigops we're willing to relay/mine in a single tx */
 static constexpr unsigned int MAX_STANDARD_TX_SIGOPS_COST{MAX_BLOCK_SIGOPS_COST/5};
-/** Default for -incrementalrelayfee, which sets the minimum feerate increase for mempool limiting or BIP 125 replacement **/
+/** Default for -incrementalrelayfee, which sets the minimum feerate increase for mempool limiting or replacement **/
 static constexpr unsigned int DEFAULT_INCREMENTAL_RELAY_FEE{1000};
 /** Default for -bytespersigop */
 static constexpr unsigned int DEFAULT_BYTES_PER_SIGOP{20};
diff --git a/src/policy/rbf.cpp b/src/policy/rbf.cpp
index d15946de21..6098caced9 100644
--- a/src/policy/rbf.cpp
+++ b/src/policy/rbf.cpp
@@ -65,7 +65,7 @@ std::optional<std::string> GetEntriesForConflicts(const CTransaction& tx,
     uint64_t nConflictingCount = 0;
     for (const auto& mi : iters_conflicting) {
         nConflictingCount += mi->GetCountWithDescendants();
-        // BIP125 Rule #5: don't consider replacing more than MAX_REPLACEMENT_CANDIDATES
+        // Rule #5: don't consider replacing more than MAX_REPLACEMENT_CANDIDATES
         // entries from the mempool. This potentially overestimates the number of actual
         // descendants (i.e. if multiple conflicts share a descendant, it will be counted multiple
         // times), but we just want to be conservative to avoid doing too much work.
@@ -96,7 +96,7 @@ std::optional<std::string> HasNoNewUnconfirmed(const CTransaction& tx,
     }
 
     for (unsigned int j = 0; j < tx.vin.size(); j++) {
-        // BIP125 Rule #2: We don't want to accept replacements that require low feerate junk to be
+        // Rule #2: We don't want to accept replacements that require low feerate junk to be
         // mined first.  Ideally we'd keep track of the ancestor feerates and make the decision
         // based on that, but for now requiring all new inputs to be confirmed works.
         //
@@ -162,7 +162,7 @@ std::optional<std::string> PaysForRBF(CAmount original_fees,
                                       CFeeRate relay_fee,
                                       const uint256& txid)
 {
-    // BIP125 Rule #3: The replacement fees must be greater than or equal to fees of the
+    // Rule #3: The replacement fees must be greater than or equal to fees of the
     // transactions it replaces, otherwise the bandwidth used by those conflicting transactions
     // would not be paid for.
     if (replacement_fees < original_fees) {
@@ -170,7 +170,7 @@ std::optional<std::string> PaysForRBF(CAmount original_fees,
                          txid.ToString(), FormatMoney(replacement_fees), FormatMoney(original_fees));
     }
 
-    // BIP125 Rule #4: The new transaction must pay for its own bandwidth. Otherwise, we have a DoS
+    // Rule #4: The new transaction must pay for its own bandwidth. Otherwise, we have a DoS
     // vector where attackers can cause a transaction to be replaced (and relayed) repeatedly by
     // increasing the fee by tiny amounts.
     CAmount additional_fees = replacement_fees - original_fees;
diff --git a/src/policy/rbf.h b/src/policy/rbf.h
index f3efcebbe0..09c495506a 100644
--- a/src/policy/rbf.h
+++ b/src/policy/rbf.h
@@ -19,7 +19,7 @@
 class CFeeRate;
 class uint256;
 
-/** Maximum number of transactions that can be replaced by BIP125 RBF (Rule #5). This includes all
+/** Maximum number of transactions that can be replaced by RBF Rule #5. This includes all
  * mempool conflicts and their descendants. */
 static constexpr uint32_t MAX_REPLACEMENT_CANDIDATES{100};
 
@@ -47,24 +47,25 @@ enum class RBFTransactionState {
 RBFTransactionState IsRBFOptIn(const CTransaction& tx, const CTxMemPool& pool) EXCLUSIVE_LOCKS_REQUIRED(pool.cs);
 RBFTransactionState IsRBFOptInEmptyMempool(const CTransaction& tx);
 
-/** Get all descendants of iters_conflicting. Also enforce BIP125 Rule #5, "The number of original
- * transactions to be replaced and their descendant transactions which will be evicted from the
- * mempool must not exceed a total of 100 transactions." Quit as early as possible. There cannot be
- * more than MAX_REPLACEMENT_CANDIDATES potential entries.
+/** Get all descendants of iters_conflicting. Checks that there are no more than
+ * MAX_REPLACEMENT_CANDIDATES potential entries. May overestimate if the entries in
+ * iters_conflicting have overlapping descendants.
  * @param[in]   iters_conflicting   The set of iterators to mempool entries.
  * @param[out]  all_conflicts       Populated with all the mempool entries that would be replaced,
- *                                  which includes descendants of iters_conflicting. Not cleared at
- *                                  the start; any existing mempool entries will remain in the set.
- * @returns an error message if Rule #5 is broken, otherwise a std::nullopt.
+ *                                  which includes iters_conflicting and all entries' descendants.
+ *                                  Not cleared at the start; any existing mempool entries will
+ *                                  remain in the set.
+ * @returns an error message if MAX_REPLACEMENT_CANDIDATES may be exceeded, otherwise a std::nullopt.
  */
 std::optional<std::string> GetEntriesForConflicts(const CTransaction& tx, CTxMemPool& pool,
                                                   const CTxMemPool::setEntries& iters_conflicting,
                                                   CTxMemPool::setEntries& all_conflicts)
     EXCLUSIVE_LOCKS_REQUIRED(pool.cs);
 
-/** BIP125 Rule #2: "The replacement transaction may only include an unconfirmed input if that input
- * was included in one of the original transactions."
- * @returns error message if Rule #2 is broken, otherwise std::nullopt. */
+/** The replacement transaction may only include an unconfirmed input if that input was included in
+ * one of the original transactions.
+ * @returns error message if tx spends unconfirmed inputs not also spent by iters_conflicting,
+ * otherwise std::nullopt. */
 std::optional<std::string> HasNoNewUnconfirmed(const CTransaction& tx, const CTxMemPool& pool,
                                                const CTxMemPool::setEntries& iters_conflicting)
     EXCLUSIVE_LOCKS_REQUIRED(pool.cs);
@@ -90,9 +91,8 @@ std::optional<std::string> EntriesAndTxidsDisjoint(const CTxMemPool::setEntries&
 std::optional<std::string> PaysMoreThanConflicts(const CTxMemPool::setEntries& iters_conflicting,
                                                  CFeeRate replacement_feerate, const uint256& txid);
 
-/** Enforce BIP125 Rule #3 "The replacement transaction pays an absolute fee of at least the sum
- * paid by the original transactions." Enforce BIP125 Rule #4 "The replacement transaction must also
- * pay for its own bandwidth at or above the rate set by the node's minimum relay fee setting."
+/** The replacement transaction must pay more fees than the original transactions. The additional
+ * fees must pay for the replacement's bandwidth at or above the incremental relay feerate.
  * @param[in]   original_fees       Total modified fees of original transaction(s).
  * @param[in]   replacement_fees    Total modified fees of replacement transaction(s).
  * @param[in]   replacement_vsize   Total virtual size of replacement transaction(s).