There’s a bunch of interesting stuff if you dive into the Coda.app package: (Contents > Resources > Modes > CSS.mode > Contents > Resources
)
Namely AutocompleteAdditions.txt and CodaCompletion.plist. I wanted to add every proprietary WebKit CSS property but it looks like a lot of work. I did one and Coda didn’t necessarily recognize it. However, in the same folder, SyntaxDefinition.xml has almost all of them listed.
Hopefully Panic Inc. can get to them soon.