Hmm. Just checked again. Two of the expressions match neither word, one matches both, and one matches only one.

EDIT: I see. The confusion is over partial match vs whole match. I thought whole matches were standard when talking about regular expression in the abstract, but looks like I was wrong. Just changed the problem to include the anchors. Thanks for pointing this out.

That's not the standard meaning in my experience. Regex's are often used for extracting information from larger strings, forcing a full match by default would be pretty counter to their purpose.

Yep, I just came here to post that:

In [2]: re.search("b[l].e", "babel")

In [3]: re.search("b[l].e", "blabber") Out[3]: <_sre.SRE_Match at 0x7f2db79ed030>

It looks like they meant "match" as in "re.match", i.e. "^b[l].*e$", which is not the usual definition of the word.

That would also make this question specific to python, which wasn't at all what I was thinking about. It's a question about regular expressions, it should be as agnostic as possible to implementation.

Yeah, agreed, although there are different RE flavors, so you can't get too agnostic.