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"(?<!\d) (?: [0-9]{4} (?P<sep1>[-/.])? (?: (?:(?(sep1)0?|0)[1-9]|1[0-2]) (?(sep1)(?P=sep1)|) (?:(?(sep1)0?|0)[1-9]|1[0-9]|2[0-8]) |(?:(?(sep1)0?|0)[13-9]|1[0-2]) (?(sep1)(?P=sep1)|) (?:29|30) |(?:(?(sep1)0?|0)[13578]|1[02]) (?(sep1)(?P=sep1)|) (?:31) ) | (?: [0-9]{2} (?: 0[48] |[2468][048] |[13579][26] ) |(?: 0[48] |[2468][048] |[13579][26] )00 ) (?P<sep2>[-/.]?) (?(sep2)0?|0)2 (?(sep2)(?P=sep2)|) (?:29) ) (?!\d) "gmxPython+16 years ago✓ Pre-loaded

About this regex

This complex regex matches valid calendar dates in formats like YYYY-MM-DD, YYYY/MM/DD, or YYYYMMDD. It validates month/day combinations (e.g., Feb 29 only in leap years) and optionally enforces consistent separators. Key features include conditional patterns based on separator presence and lookahead/lookbehind to avoid partial matches in longer digit sequences.

date validation calendar leap-year format-check

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About this regex

date validation calendar leap-year format-check

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