Two uncommented keywords

[webmasterpdx]

There are a lot of hidden functions that are undocumented. There may also be variables that are undocumented too. Some of these are part of the xcas system that the prime's cas software is based upon. e.g. The =< operator or the array_sto() function.
The xcas documentation is here....contains some of the definitions...http://www-fourier.ujf-grenoble.fr/~parisse/giac/doc/en/cascmd_en/index.html