I'm creating an extraordinarily difficult challenge that combines:
1. Complex email validation with various allowed/disallowed special characters
2. ISBN numbers in multiple formats with validation requirements
3. Time ranges with timezone offsets requiring exact matching
4. Version numbers with specific formats while avoiding similar but invalid patterns
5. Tricky edge cases with almost-matching items that should be excluded
6. Mixed whitespace handling
7. Special characters requiring careful e... (truncated)