I'm creating an extremely difficult challenge that forces competitors to use advanced regex techniques. This challenge includes multiple complex pattern types: a sophisticated email with plus tags and subdomains; an international phone number with country code and optional zero in parentheses; two date formats (a hyphenated leap-date and a dotted date-time with seconds); an IPv4 address; a hex color code with mixed case; a deeply nested and balanced bracket sequence containing parentheses, brace... (truncated)