Does a plug-in exist, or could one be created, that allows for document review/change tracking similar to that found in MS Word? In MS Word multiple users can collaborate on a document and each make changes that are kept track of by Word. Everyone's mark-ups show in a different color and additions/deletions are clearly shown as strikethroughs, etc. Is there a plugin that would do something similar in WordPress so that several people could do collaborative editing on a blog?