I was looking for a module that deals with checking whether a given IPv4 address is contained within a netblock. There are several modules out there (that I have used in the past) that do just this, and I couldn't remember their exact names.
So I ran a search, and noticed this module, which sounds like it does exactly what I was looking for, and nothing else.
Looking at the documentation, it offers a single function, which returns a true/false value. Unfortunately, the name of the function is __MATCH_IP, which, apart from the screaming uppercase, may also be considered a private function since it begins with an underscore. The rationale for this choice is not explained.
This seemed sufficiently odd for me to pass it over, and look for something else. Looking more closely, the test suite does not try to explore the problem space very much.