Regex Tester & Validator

Matches the literal string 'grey ' (with trailing space) only when it is immediately followed by one or more lowercase letters. The positive lookahead (?=[a-z]+) is zero-width, so it asserts that lowercase text follows without consuming it, meaning the overall match is just 'grey ' itself. This is useful for finding 'grey' only when it precedes a lowercase word (e.g., 'grey cat', 'grey area') and serves as a classic example of lookahead usage. With the g flag, all occurrences in the input are found.