code: func (s *Schema) Index(name string, options ...IndexOption) *Index {
  	if index, ok := s.indexes[name]; ok {
  		return index
  	}
  	indexOptions := &IndexOptions{}
  	indexOptions.addOptions(options...)
  	return s.indexWithOptions(name, 0, indexOptions)
  }
docs: // Index returns an index with a name.