function waterfall() {
		var idx = -1;
		next(); // eslint-disable-line node/callback-return

		/**
		* Executes the next function in the series.
		*
		* @private
		* @param {(Error|null)} error - error object
		* @param {...*} args - results to pass to next callback
		* @returns {void}
		*/
		function next() {
			var args;
			var len;
			var i;

			// Check for an error...
			if ( arguments[ 0 ] ) {
				return clbk( arguments[ 0 ] );
			}
			// Update the counter and check if we have run all functions...
			idx += 1;
			if ( idx >= fcns.length ) {
				return clbk();
			}
			// Copy the remaining arguments...
			len = arguments.length;
			args = new Array( len );
			for ( i = 0; i < len-1; i++ ) {
				args[ i ] = arguments[ i+1 ];
			}
			// Add the callback:
			args[ i ] = next;

			// Apply the arguments to the next function in the waterfall:
			fcns[ idx ].apply( thisArg, args );
		}
	}
Executes functions in series, passing the results of one function as arguments to the next function.

@private