number/interpreted mathematical object non-restrictive clause
It first terminates the immediately preceding expression and immediately forces its interpretation as a mathematical object as far as possible (so an unmodified PA*, BY*, or SYM* constuct (string) is terminated (as by boi) and then understood as a number/word; operators are understood as objects as well). Thn it introduces a restrictive relative clause in which ke'a refers to the immediately preceding object. This differs from the PA relative clause markers in that it forces the interpretation of the string as much as possible and the resulting meaning/object is the subject. It interprets the maximal immediately preceding string.