code: func (a *APIDefinition) MediaTypeWithIdentifier(id string) *MediaTypeDefinition {
  	canonicalID := CanonicalIdentifier(id)
  	for _, mt := range a.MediaTypes {
  		if canonicalID == CanonicalIdentifier(mt.Identifier) {
  			return mt
  		}
  	}
  	return nil
  }
docs: // MediaTypeWithIdentifier returns the media type with a matching
  // media type identifier. Two media type identifiers match if their
  // values sans suffix match. So for example "application/vnd.foo+xml",
  // "application/vnd.foo+json" and "application/vnd.foo" all match.