I think HTML obviously is allowed to call something "pure CSS," since an HTML document is required to even load CSS, and CSS rules can only apply to DOM elements. JavaScript, however, shouldn't be allowed.
XSLT is typically used to translate XML into HTML. Sure, you could use CSS to style XML, but I believe the point isn't to argue the semantics of the markup, only to say that some sort of markup is required in order to use CSS.