code: func RegisterDialerType(scheme string, f func(*url.URL, Dialer) (Dialer, error)) {
  	if proxySchemes == nil {
  		proxySchemes = make(map[string]func(*url.URL, Dialer) (Dialer, error))
  	}
  	proxySchemes[scheme] = f
  }
docs: // RegisterDialerType takes a URL scheme and a function to generate Dialers from
  // a URL with that scheme and a forwarding Dialer. Registered schemes are used
  // by FromURL.