Regex handoff: document pattern, flags, and limits

A regex handoff should include the expression, engine or language, flags, expected full or partial match behavior, and a labeled test set. Explain what the pattern deliberately does not validate. If it is used in replacement, show before-and-after output and check capture groups. For untrusted input, note maximum length and any performance test. This lets the next reviewer reproduce the behavior instead of guessing how a screenshot of highlighted text was produced.