code: function(index) {
  			Y.log("Fetching key at " + index);
  
  			if (YL.isNumber(index) && -1 < index && this.length > index) {
  				var value = this._key(index);
  				if (value) {return value;}
  			}
  
  			// this is thrown according to the HTML5 spec
  			throw('INDEX_SIZE_ERR - Storage.setItem - The provided index (' + index + ') is not available');
  		}
docs: Retrieve the key stored at the provided index; should be overwritten by storage engine.
  @method key
  @param index {Number} Required. The index to retrieve (unsigned long in HTML 5 spec).
  @return {String} Required. The key at the provided index (DOMString in HTML 5 spec).
  @public