The attribute revisionflag
is usefull to identify the changes between two revisions of a document. This information is managed by dblatex, that adds revision bars in the margin of the paragraphs changed, such like in this paragraph.
Adding the revision flags can be manual, but its is tedious and error prone. The perl script diffmk by Norman Walsh can do the work for you. It works fine, but it depends on several Perl modules.
With old changebar packages the revision bars only appear when using the "dvips" driver. This limitation has been fixed with changebar greater or equal to v3.5c.