x1 is unnecessary Lojban jargon for natural-language equivalent term x2
Ex.: zo'oi «modal» valcrimtu zo'oi «preposition». "Modal" or sumtcita instead of "preposition", selbri instead of "main verb" and so on. Refers to using Lojban jargon for discussing grammar when there's perfectly good English words that mean the same and aren't as opaque.