Point at a node, or at a piece of the pattern; the arrow keys walk the tree.
Point at a node to read it.
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Runs on php-wasm (Apache-2.0) with mbstring and oniguruma (BSD), loaded from jsDelivr when you press Run. The Step through tab traces the match with PCRE2 itself (BSD-3-Clause), compiled to WebAssembly without a change.