This is a nice way to edit two or three different versions of a file. Changed lines are highlighted. A change within a line is highlighted differently, so that you can spot an inserted word, for example.
Folding is used to hide the text that has no changes.
It's still new, there could be a few problems. It's standard on Unix, for other systems you will have to find it somewhere. Added the vimdiff command to start diff mode on a few files. - Added the vimdiff manpage. The 'patchexpr' option can be set to patch a file with an expression. Included the QNX port.