I'm creating an extraordinarily difficult challenge that combines:
1. Complex nested patterns with mixed formats
2. Items requiring negative lookaheads to avoid false matches
3. Various date/time formats with microsecond precision
4. Tricky ISBN-like codes with checksums
5. Base64-encoded tokens with specific patterns
6. Email addresses with complex requirements
7. Similar but invalid patterns that should be excluded
This will require extensive use of lookarounds, backreferences, and precise bou... (truncated)