Date validate question.

I am using Illustra with Web Data Blade. It seems that there is no easy way to accept a date from a web page and determine if it is a valid date. (Apply a date edit). I would expect a $(ISDATE,value) function but there is none. Also there seems to be no date validation function in the Illustra User's Guide. Am I missing something? How the heck do I go about validating a date other than trying some other date function on it and letting it throw an error or writing my own date edit routine. There MUST be some standard way of doing this. Thanks, Mike