How to highlight changes when comparing versions of a document in OS X?

I've been exploring the versions functionality of the new document model in Mac OS X 10.8. It's mostly similar to what was in Lion. In the title bar of a supported document choose "Browse all versions…" from the drop-down menu. It seems handy enough, but how can you easily tell what has changed between each document without having to manually scan each line? I assumed there must be a feature to highlight the changes but I can't find it. Has anyone figured this out?