how do you delete a list from a program

[webmasterpdx]

I found out how to do this finally in an obscure post via google.
purge(name) works for CAS variables.
For system builtin variables, use L1:={} to clear out the variable, but the variable itself can't be deleted.
For home user variables, or from a program, you can delete them using DelHVars("name").
This delete command doesn't appear to be documented anywhere. However it works. The quotes are necessary.