Regex lookahead and lookbehind are zero-width assertions that match positions without consuming characters. Positive lookahead checks what follows. Negative lookahead checks what does not follow. Lookbehind assertions check what precedes the current position. These advanced patterns are essential for password validation, data extraction, and complex search-and-replace operations.
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Regex Lookahead & Lookbehind
Master regex lookahead (?=), lookbehind (?<=), and their negative variants.
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