13. Booleans
The quick reference guide is on page 208 of the PDF.
Summary
- 
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 
Extras
replicatestring-contains?