code: function makeFormatter(aFragments) {
  		var fnFormatter = function() {
  				var aResult = [],
  					l = aFragments.length,
  					i;
  
  				for (i = 0; i < l; i++) {
  					if ( typeof aFragments[i] === "number" ) {
  						// a numerical fragment references the part with the same number
  						aResult.push(arguments[aFragments[i]]);
  					} else {
  						// anything else is a string fragment
  						aResult.push(aFragments[i]);
  					}
  				}
  				return aResult.join('');
  			};
  		fnFormatter.textFragments = aFragments;
  		return fnFormatter;
  	}
docs: Helper to create a formatter function. Only used to reduce the closure size of the formatter
  
  @param {number[]|string[]} aFragments
  array of fragments, either a literal text or the index of the binding's part
  @returns {function}
  a formatter function