+/**
+ * Register importer for WordPress.
+ *
+ * @since 2.0.0
+ *
+ * @param string $id Importer tag. Used to uniquely identify importer.
+ * @param string $name Importer name and title.
+ * @param string $description Importer description.
+ * @param callback $callback Callback to run.
+ * @return WP_Error Returns WP_Error when $callback is WP_Error.
+ */