I’ve been playing around with flex for a while now. I was able to setup a compile environment under liux using emacs, a Makefile.
I also found a mode for emacs to highlight actionscript 3 files here. It missed a hook, which will automatically set the actionscript-mode if a file of extension .as was loaded & could not find a way to comment on their blog, so it’s here for reference.
(setq auto-mode-alist (cons ‘(“\\.as$” . actionscript-mode) auto-mode-alist))