x1 is a nonsense zei-lujvo using parts x2, silly by standard x3.
This lujvo parses in jbofi'e as an artifact of how high precedence zei is, and how zo erasure works. Specifically, [zo WORD si] has not erased the entire zo clause but has killed zo's "magic". fa'o and quoted si are replaceable, but thrown in for fun, to have a full magic-word lujvo.