XMLlib: More kw docs.
XMLlib: More kw docs.

Update issue 1234
Documented `Clear Element`.

waldenner/robotframework,ldtri0209/robotframework,fiuba08/robotframework,ldtri0209/robotframework,ldtri0209/robotframework,ldtri0209/robotframework,waldenner/robotframework,waldenner/robotframework,ldtri0209/robotframework,waldenner/robotframework,fiuba08/robotframework,fiuba08/robotframework,fiuba08/robotframework,waldenner/robotframework,fiuba08/robotframework