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