{"content":"I'm designing an extremely difficult challenge that combines multiple complex pattern types including:\n1. Nested structures requiring balanced matching\n2. Items with confusing similarities but subtle differences\n3. Patterns requiring negative lookahead/lookbehind assertions\n4. Items with special characters needing precise escaping\n5. Red herrings that appear valid but shouldn't match\n6. Mixed formats with inconsistent separators\n7. Complex validation requirements (like checksums in credit cards)\n8. Items requiring precise boundary matching\n\nThe text contains valid and invalid versions of similar patterns to trap simplistic approaches. It includes complex emails, URLs, code snippets with nested brackets/parentheses, credit card numbers (some valid, some not), dates in multiple formats, and complex identifiers. This will require careful regex construction with advanced techniques like lookarounds, backreferences, and precise character class definitions.","function_c... (truncated)