The quick reference guide is on page 208 of the PDF.
Functions end in ?
if (and only if) they return a boolean value for their answer.
true, false
Determine the type of something: string?, number?, integer?, image?, boolean?
Decide equality: string=?
, image=?
, etc.
Comparisons for numbers: <
, <=
, =
, >=
, >
Comparisons for other things: string<?
, string<=?
, string=?
, etc.
Case insensitive comparison: string-ci<?
, etc.
Combinations: and
, or
, not
replicate
string-contains?