This fixes some mistakes in the python pseudocode (that described an older version that is not aligned to the draft implementation in core), and fixes some minor other details.
Commit e4e2b7ccd10af0ad0fdab6358461567326ee21e8 also adds a paragraph to clarify that fees are expected to be paid exogenously. While not specific to CCV and rather common to most/all covenant proposals, it was suggested in the comments of the previous PR to have an explainer (cc @Sjors).
ignore footgun warning is especially useful.
175@@ -176,7 +176,7 @@ would always be hard-coded via a push in the script, the risk of mistakes seems
176
177 The following values of the other parameters have special meanings:
178 * If the <code><taptree></code> is -1, it is replaced with the Merkle root of the current input's tapscript tree. If the taptree is the empty buffer, then the taptweak is skipped.
179-* If the <code><pk></code> is 0, it is replaced with the NUMS x-only pubkey <code>0x50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0</code> defined in [[bip-0340.mediawiki|BIP-340]]. If the <code><pk></code> is -1, it is replaced with the taproot internal key of the current input.
180+* If the <code><pk></code> is 0, it is replaced with the NUMS x-only pubkey <code>0x50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0</code> defined in [[bip-0341.mediawiki|BIP-341]]. If the <code><pk></code> is -1, it is replaced with the taproot internal key of the current input.
224@@ -209,7 +225,7 @@ def tweak_embed_data(pubkey, data):
225 return 0 if has_even_y(Q) else 1, bytes_from_int(x(Q))
226 </source>
227
228-The <code>taproot_tweak_pubkey</code> from [[bip-0341.mediawiki|BIP-341]] is also used as a helper function.
229+The <code>taproot_tweak_pubkey</code> function is also used as a helper in the pseudocode below.
Anti-footgun: perhaps add for clarity something like this?
0The <code>taproot_tweak_pubkey</code> function (the variant specified in this BIP, as opposed to the one in BIP-341) is also used as a helper in the pseudocode below.
taproot_tweak_pubkey is used verbatim as defined in BIP-341 in the following line of the pseudocode:
_, final_key = taproot_tweak_pubkey(internal_key, taptree)
tweak_embed_data is its variant defined in this BIP.
In other words, CCV applies (up to) two tweaks; the first one is the tweak_embed_data variant for data embedding, while the second tweak is identical to BIP-341 – which is necessary, or it would be incompatible with P2TR.