For some reason, I always have trouble finding and download the Flash ActionScript 3 language documentation. The LiveDocs are easy to find, but the zipped documentation – which is super useful to have locally for faster access and for quick help at the press of F1 if you install it on a tool like FDT – is somehow difficult to find if you just use Google to look for it (too much noise).
Plus, the official reference page contains a Zip package that is out-of-date (from 2008!). Grrrr (Edited at August 11th, 2011: apparently this page has been removed and now redirects to the Flash Help online index).
Anyway, the direct link to the archived AS3 reference files seems to be this. Thanks to @sfdesigner for coming up with this mysterious link. The source page for this link seems to be the ActionScript reference archive.
Hopefully this will be helpful to some other people out there (and I’m naively hoping posting this here will help Google and other search engines take people to the right link).
Bonus: the Flex 4.5 API beta reference (for Flash 11) can be found here, although there’s no download option yet.
Anyway, this is all to say that if you want the documentation to work properly in FDT, you have no option other than getting a copy of the Flash documentation and using it instead. This page contains such a copy that is moderately up-to-date (August 2010), and it’s what I’m using on FDT now.
Update for FDT users (July 1st, 2013): FDT has been updated with a fix that allows uses to import the “standalone.zip” file directly, instead of trying to read the Flash IDE help format. Just go to the help settings window and import the downloaded file.