Not a valid AllXsd value

Today I was programming a PHP client that uses an XML-RPC web service. One of the fields the service requires is a date/time field as an AllXsd value. When you give the field a date in any other format it returns the error: Not a valid AllXsd value. What the heck is that?? How did anyone program before search engines and the Internet?

The format it requires is:


To generate a valid AllXsd value for a date time using PHP is extremely easy: