#utility Prompts

Prompt - Regex Pattern Builder and Explainer

Act as a regex expert. I need a regular expression that [DESCRIBE WHAT TO MATCH]. Examples that should match: [LIST]. Examples that should NOT match: [LIST]. Give me the regex, explain each part in plain English, note the flavor (PCRE/JS/Python), warn about edge cases and catastrophic backtracking, and provide a quick test snippet. Keep it as simple as the requirement allows.