code: function apply_methods(Class, methods, descriptor) {
             Object.keys(descriptor).forEach(function (method) {
                 methods[method] = descriptor[method];
  
                 if (typeof(descriptor[method]) !== "function") {
                     throw new TypeError(
                         "extend: Method `" + method + "` is not a function"
                     );
                 }
  
                 Object.defineProperty(Class.prototype, method, {
                     "configurable" : true,
                     "value" : descriptor[method]
                 });
             });
         }
docs: Apply methods to the class prototype.
  @ignore