Computer script is kind of a broad term, but my guess would be a web script, given they want to use it in conjunction with HTML.
I'm sure we both know why PHP wasn't working for them... common beginner mistake to try to use it as client side code
And XML is out on account of not really being a language per se but rather a way to store hierarchical data; thus begging the question what the use of data will be without something to parse it.
XHTML on the other hand, now that could be a different story.