It depends on what you mean by "git client" I guess. Generally speaking, git clients are just handling file versioning and don't really care whether the file is a binary blob or an rtf file, of a plain text file. Xcode is a text editor with VC included. The diff view you mention could potentially be available to any git client that uses a diff viewer that supports (or rather ignores) rich text. But when any other git client would check that file, it would still see the RTF code.