Of course, its a jquery expression, what else... However, I do think the docs may be wrong: at http://docs.jquery.com/Plugins/Validation/Methods/required#dependency-expression
In the arguments section it reads: "An expression (String) is evaluated in the context of the element's form, making the field required only if the expression returns more than one element." Surely that should be "one or more elements"? Regards - Iwan