The current regex syntax and match highlighting system of using <pre> elements underneath <textarea> elements to contain the highlighting (paired with a container whose scrollbars are used for seemless scrolling) is very fast but unfortunately too brittle / quirky / buggy to work well across all A-grade browsers. A more traditional contentEditable / designMode -based highlighting system might be a pain to set up and will almost certainly be slower, but it would be more flexible and help to get rid of several lingering bugs.