function command( pres ) {
	return onCommand;

	/**
	* Renders the current presentation slide.
	*
	* @private
	* @returns {(string|null)} rendered slide
	*/
	function onCommand() {
		return pres.render();
	}
}
Returns a callback to be invoked upon calling the `renderSlide` command.

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