A basic input editor should be created for the "content" property as a sort of placeholder until a more comprehensive editor is created (the list of valid values for "content" is crazy and has so many different options).
Created attachment 268678 [details] Patch
Comment on attachment 268678 [details] Patch Clearing flags on attachment: 268678 Committed r194876: <http://trac.webkit.org/changeset/194876>
All reviewed patches have been landed. Closing bug.