How to get a variables name

["Stefan Harwarth" <stefan@harwarth.de>]

Hello,
I'm relativly new to PARI and need to fetch the name of a variable from the
"variable number" (something like a reverse fetch_user_var()) in library
mode.

In the User Manual in chapter 4.6.1 I found nothing useful except the
reference to the field varentries[] and after a short glance into the code
the struct-member "name", but since it is not in the documentation, I fear
that it might change in the future.

Is there any documented function for this task?

Stefan Harwarth