How do I edit or add to Notepad++ HTML/CSS autocomplete?

Could anyone tell me how to go about editing the existing CSS and/or HTML autocomplete language in Notepad++? My Google-fu has let me down and I can't find an answer.

In essence, I want to add some CSS3 to the autocomplete and to edit some of the existing entries to suit my needs.

I'm using v.5.7 on Win7 btw.

I think you can just add the relevant new keywords to the langs.xml file within the Notepad++ directory (back it up first, the usual warnings, etc). But, I believe this will do syntax highlighting only.

So, if you then go in to the plugins\APIs subdirectory you can edit the relevant .xml to also provide auto completion.