function command( pres ) {
	return onCommand;

	/**
	* Proceeds to the previous presentation slide or slide fragment.
	*
	* @private
	*/
	function onCommand() {
		pres._repl.once( 'drain', onDrain ); // eslint-disable-line no-underscore-dangle

		/**
		* Callback invoked upon a `drain` event.
		*
		* @private
		*/
		function onDrain() {
			pres.prev().show();
		}
	}
}
Returns a callback to be invoked upon calling the `prev` command.

@private
@param {Presentation} pres - presentation instance
@returns {Function} callback