Generally undocumented commands are risky to use - they may (and often do) disappear between releases. If you do find one that you regard as being necessary you should raise an enhancement request to get it made "public".
Of course, because they are undocumented, you will have to guess the command syntax. Easy for some commands but not others. However, using the command: arglist usually helps.
The trick for finding them is to search the symbols used in the lisp symbol list: oblist.
I'll post some code over in the Skill forum.