code: func (idx *Index) Field(name string, options ...FieldOption) *Field {
  	if field, ok := idx.fields[name]; ok {
  		return field
  	}
  	fieldOptions := &FieldOptions{}
  	fieldOptions = fieldOptions.withDefaults()
  	fieldOptions.addOptions(options...)
  	return idx.fieldWithOptions(name, fieldOptions)
  }
docs: // Field creates a Field struct with the specified name and defaults.