regexp.go
func (m *RegexpPath) Extract(result *Result, r *http.Request) {
	result.Values = mergeValues(result.Values, m.Values(r.URL.Path))
}
func (m *RegexpPath) Extract(result *Result, r *http.Request) {
	result.Values = mergeValues(result.Values, m.Values(r.URL.Path))
}
// Extract returns positional and named variables extracted from the URL path.