Anonymous monk, and that is precisely where that is being placed, inside of a one liner utility subroutine, that is documented as to what it tests, in this case, it returns 1, true, if the match is correct, and undefined, false, if not. As part of a larger test, but as a one liner. I have used arcane syntax like this internally in utility tools, and try to keep it out of the main logic that would be likely to get patches or pull requests. Documented, with comments, etc.
Now that this is confirmed safe, I'll be extending its use for all numeric tests (which is what this particular case is doing), and look into more secret type constructions for various utilities, that are not meant to be end user readable or serviceable, but are meant to be very very fast.