code: func (m *GorillaPathPrefix) Build(u *url.URL, values url.Values) error {
  	path, err := m.RevertValid(values)
  	if err == nil {
  		u.Path = path
  	}
  	return err
  }
docs: // Build builds the URL path using the given positional and named variables,
  // and writes it to the given URL.