Description:
------------
What we often need to test for is just whether a substring exists or 
not. For example this is very common in examining a user agent.

Currently you can use strpos, but you have to be careful to test only 
with two specific formulations, using the strict equivalency 
operators:

	if (strpos($x, $y) === FALSE)

or

	if (strpos($x, $y) !== FALSE)


That "anti-FALSE" approach is generally awkward, and if you use == or 
!= by mistake you'll have ambiguity with a substring position of 
number 0.


It would be handy and much less prone to syntax mistakes, to have a 
dedicated "string exists" function which returns only TRUE or FALSE.

This might be "strex" or "strpres" ("string present").

Plus an equivalent case sensitive version -- striex or stripres.