code: func ByScheme(scheme string, settings environment.EnvSettings) (Provider, error) {
  	// Q: What do you call a scheme string who's the boss?
  	// A: Bruce Schemestring, of course.
  	a := All(settings)
  	for _, p := range a {
  		if p.Provides(scheme) {
  			return p, nil
  		}
  	}
  	return Provider{}, fmt.Errorf("scheme %q not supported", scheme)
  }
docs: // ByScheme returns a getter for the given scheme.
  //
  // If the scheme is not supported, this will return an error.