Function match_url 

pub fn match_url(
    template: &str,
    url: &str,
    known_representation_ids: &[&str],
) -> Option<TemplateMatch>

Recover the identifiers that substitute would have rendered as url.

known_representation_ids supplies the values $RepresentationID$ may take; they are tried longest-first and the whole url must match. Returns None when the template is invalid (any TemplateFault), when a $SubNumber$ makes the reading undefined, or when the reading is not unique.