Question 1

What regex flavour does this tool use?

Accepted Answer

JavaScript regex (ECMAScript). Flags supported: g (global), i (case-insensitive), m (multiline, ^ and $ match line boundaries), s (dotAll, . matches newlines), u (Unicode mode). Lookahead/lookbehind are supported in ES2018+ (all modern browsers).

Question 2

What is the difference between .test() and .match()?

Accepted Answer

RegExp.test(str) returns a boolean — does the pattern match? String.match(regex) returns the matched substrings (or null). This tool shows both: whether a match exists and all matched groups/captures highlighted in the text.

Question 3

Why does my regex match nothing in multiline text?

Accepted Answer

Without the m flag, ^ anchors to the very start of the string and $ to the very end. With the m flag, ^ and $ match at every line start/end. If you're matching line-by-line patterns, add the m flag.

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