I dont' really like adding new vars that can be either a string or a list of tuples.

We did it in the past, but also deprecated these things because we will fix them in 2.0
I would prefer having something like 2 optional vars, 
the cmd one, and it can be ignored if the regex_template var is given wich is a list of tuples.

Because now you have to check instances etc, which is a bit ugly, because it breaks the ducktyping system.