On grammatical class:

na'u
convert selbri to mex operator; used to create less-used operators using fu'ivla, lujvo, etc.

In definition:

cmavrna'u
x1 is the selma'o "NAhU".

In notes:

mekseia
x1 is a part of Lojban text representing rule 'mex-operator' according to the first edition of the book 'The Complete Lojban Language'.