Manually comparing versions of a long XML Schema or document to find any differences would be a tedious and error-prone task. XMLSpy has long featured file comparison with highlighted differences in side-by-side windows with merging in either direction. And of course, DiffDog is the go-to comparison utility for text, source code, XML, JSON, and Word documents. Now both XMLSpy and DiffDog support three-way file comparison and difference merging.
Three-way file comparison is especially relevant for files managed in any source control system where two users may have started from the same source file and made different edits that need to be reconciled.