as3syntaxhighlight is a port of google-code-prettify (which incidentally is what google code uses to highlight code) to ActionScript. It supports syntax highlighting of code in a variety of programming languages including MXML and AS3. It can be used for syntax highlighting as you type or for generating HTML which can be applied as htmlText to a TextField or TextArea. It also features an AS3 specific "async" mode that allows it to work in chunks without blocking the UI.

To read up more about the library and to check out a live demo, visit this link.

This library was developed for sandboxviolation.

Note: as3syntaxhighlight is 100% client side and meant to be used by Flex or Flash developers. It does not require any server side code.