You can, but it's highly suggested you don't. First off, it's a deprecated property. Second, RegExp.$1 is the 1st match of the last RegExp ran. No matter whe

You can, but it's highly suggested you don't. First off, it's a deprecated property. Second, RegExp.$1 is the 1st match of the last RegExp ran. No matter where in your page it was ran. Extensions, events, functions, wherever. In this case, it should be safe, but don't ever actually use it on your page. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Deprecated_and_obsolete_features https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...