Proposed BIP for OP_CAT

The email discusses the behavior of the OP_CAT opcode in relation to the combined size of its arguments. It states that if the combined size is greater than or equal to 520 bytes, the OP_CAT opcode immediately succeeds, similar to the behavior of the OP_SUCCESSx opcode. The email suggests that in a future soft fork, the maximum size for OP_CAT could be increased. However, this increase would require additional opcodes to validate the size of non-constant arguments. The email mentions that in many cases, only five or six extra bytes would be needed for this validation.

The email also includes a link to "https://petertodd.org" and an example of using the OP_CAT opcode with the string 'peter'[:-1]@petertodd.org.