fixup! comments

include/secp256k1_schnorrsig.h

@@ -24,7 +24,8 @@ extern "C" {
  *  Returns: 1 if a nonce was successfully generated. 0 will cause signing to
  *           return an error.
  *  Out:  nonce32: pointer to a 32-byte array to be filled by the function
- *  In:       msg: the message being verified. Can be NULL iff msglen is 0.
+ *  In:       msg: the message being verified. Is NULL if and only if msglen
+ *                 is 0.
  *         msglen: the length of the message
  *          key32: pointer to a 32-byte secret key (will not be NULL)
  *     xonly_pk32: the 32-byte serialized xonly pubkey corresponding to key32
@@ -98,7 +99,7 @@ typedef struct {
  *  abort if it fails.
  *
  *  This function only signs 32-byte messages. If you have messages of a
- *  different size (or the same size but without an context-specific tag
+ *  different size (or the same size but without a context-specific tag
  *  prefix), it is recommended to create a 32-byte message hash with
  *  secp256k1_tagged_sha256 and then sign the hash. Tagged hashing allows
  *  providing an context-specific tag for domain separation. This prevents
@@ -111,8 +112,8 @@ typedef struct {
  *       keypair: pointer to an initialized keypair (cannot be NULL)
  *    aux_rand32: 32 bytes of fresh randomness. While recommended to provide
  *                this, it is only supplemental to security and can be NULL. See
- *                BIP-340 for a full explanation of this argument and for
- *                guidance if randomness is expensive.
+ *                BIP-340 "Default Signing" for a full explanation of this
+ *                argument and for guidance if randomness is expensive.
  */
 SECP256K1_API int secp256k1_schnorrsig_sign(
     const secp256k1_context* ctx,