Optional; allows for one or more URL's providing information about this program.
An optional xml:lang attribute can be used to define the language for this element. A comprehensive list of all possible values can be found at iana.org; a more user-friendly approach is offered by this Language Subtag Lookup tool.
Two elements, at first sight comparable, shouldn't be confused:
Provides general information about this program
Aimed at students, providing information like (personalised) schedules or enabling communication with the teacher.