What regex flavour does this tool use?+
JavaScript's built-in RegExp engine. This is compatible with most modern languages, though some advanced features (like possessive quantifiers) are JS-specific.
What do the flags g, i, m, s, u, d mean?+
g = global (find all matches, not just first), i = case-insensitive, m = multiline (^ and $ match line starts/ends), s = dotAll (. matches newlines), u = Unicode mode, d = generate match indices.
How do I test for an exact string match?+
Use ^ and $ anchors: ^your exact string$. Without anchors, the regex will match your string anywhere in the text.
How do I match an email address with regex?+
A simple pattern: [a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}. For production use, HTML's built-in email validation (type='email') or a library is more reliable.