Debatable, but I do understand the concern about regex. Easy to get them wrong. As with many computing topics, takes time to understand and get comfortable with them. 
It is likely that “regular expression” in the DSP context is not regular expressions at all. Found this from years ago:DSP regular expressions (ifvar matches)
“It just uses * and ? as kind of wild card.”
This is from Xiaowei Wang back in 2015. In that thread he indicates he patched it to make it support regex – but that would apply to his own installation.
So mystery solved I think – ifvar matches support wildcards, not regex. Even the example in the help doc for ifvar implies this:
For example: %ifvar carrier matches(‘UPS*’)%.
If that were regex, it would match strings starting with UP followed by 0 or more S chars. Unlikely to be useful. A regex for this would be ‘UPS.*’
Documentation bug IMO. And would be nice if in addition to the math operators it would support regex (and maybe wildcards).