x1 is a part of Lojban text representing rule 'simple-tense-modal' according to the first edition of the book 'The Complete Lojban Language'.
Inner structure of the rule: NAhE? SE? BAI NAI? KI? | NAhE? (time space? | space time?) & CAhA KI? | KI | CUhE. For the description of the syntax see jarnezi.