jadebox - 9:56 pm on Sep 17, 2012 (gmt 0)
Isset returns false if the specified variable (or array element) has not been defined or if it has been defined but was assigned a value of null.
Isset is not a function. It is a "language construct." It sounds like I'm being pendantic to point it out, but it is important to know because you can't, for example, reference it as a variable function or pass it to a method expecting a function.