This lightweight cross-platform text editor offers syntax highlighting, code folding and language APIs for a wide range of languages, from Actionscript to XML. You can completely configure the editor to match the look-an-feel you like.

SciTE comes with code folding, code abbreviations, and facilities for building and running programs. It also has tightly integrated LUA scripting for extensibility.

• SciTE home

There are many editions of SciTE available and these have Actionscript API support:

• SciTE for Actionscript 2.0 - A version of SciTE with AS2 support, it’s based on SciTE for Actionscript 2.0 (by Meychi)
• SciTE|Flash - The original version of SciTE with Actionscript support, this project isn’t very active and other versions are usually preferred. A more recent (beta) version is available here

Scite::ASCS is the lightest Actionscript 2 IDE extended from the SciTE editor:

• ActionScript 2 code completion and navigation,
• MTASC integration (building, checking).

Features:

• can work without any project defined so it can be used as an external editor for the Flash IDE providing code completion and MTASC code checking,
• default classpathes for all projects,
• jump to class, method, property declaration,
• Macromedia mx.* classes friendly,
• preview SWF using default Flash player,
• smart Livedocs search,
• instant javadoc-like documentation generation,
• Flash MX and MX 2004 IDE integration with Flush.

More info about Scite::ASCS

Download Scite::ASCS v0.07 (alternative location)

Code completion screenshot

It should also be noted that SE|PY ActionScript Editor and lots of other projects are based on Scintilla, which powers SciTE’s syntax-highlighting.