Source

File: wp-includes/class-wp-xmlrpc-server.php

protected function _prepare_taxonomy( $taxonomy, $fields ) {
		$_taxonomy = array(
			'name'         => $taxonomy->name,
			'label'        => $taxonomy->label,
			'hierarchical' => (bool) $taxonomy->hierarchical,
			'public'       => (bool) $taxonomy->public,
			'show_ui'      => (bool) $taxonomy->show_ui,
			'_builtin'     => (bool) $taxonomy->_builtin,
		);

		if ( in_array( 'labels', $fields, true ) ) {
			$_taxonomy['labels'] = (array) $taxonomy->labels;
		}

		if ( in_array( 'cap', $fields, true ) ) {
			$_taxonomy['cap'] = (array) $taxonomy->cap;
		}

		if ( in_array( 'menu', $fields, true ) ) {
			$_taxonomy['show_in_menu'] = (bool) $_taxonomy->show_in_menu;
		}

		if ( in_array( 'object_type', $fields, true ) ) {
			$_taxonomy['object_type'] = array_unique( (array) $taxonomy->object_type );
		}

		/**
		 * Filters XML-RPC-prepared data for the given taxonomy.
		 *
		 * @since 3.4.0
		 *
		 * @param array       $_taxonomy An array of taxonomy data.
		 * @param WP_Taxonomy $taxonomy  Taxonomy object.
		 * @param array       $fields    The subset of taxonomy fields to return.
		 */
		return apply_filters( 'xmlrpc_prepare_taxonomy', $_taxonomy, $taxonomy, $fields );
	}