String manipulation contains this section which is not very clear. Does pat refer to an exact string match, e.g. removing trim_end_match("foobar", "bar") would result in "foo", or does it support some pattern matching (as the variable name would imply)? I tried it with regex, but it seems like it is not working.

trim_end_match(s, pat) - Remove suffix of s matching pat.
trim_end_matches(s, pat) - Repeatedly remove suffixes of s matching pat.
trim_start_match(s, pat) - Remove prefix of s matching pat.
trim_start_matches(s, pat) - Repeatedly remove prefixes of s matching pat.