Why are certain commands not documented?

[webmasterpdx]

e.g. I've been playing around with the =< operator, which gets translated to array_sto()
....neither of which is in the standard documentation or in the catalog. The only place I can find these is here:
https://tiplanet.org/hpwiki/index.php?ti...e/Commands
....but these operations are not explained....
Is there any official HP documentation that has this stuff properly documented?
Thx