code: function(dest){
              var parameters = Array.prototype.slice.call(arguments),
                  override, i, l;
  
              if (!dest) { dest = {}; }
  
              if (parameters.length > 2 && typeof arguments[parameters.length-1] === 'boolean') {
                  override = parameters.pop();
              }
  
              for (i = 1, l = parameters.length; i < l; i++) {
                  lang._mixin(dest, parameters[i], override);
              }
              return dest; // Object
          }
docs: mixin({}, obj1, obj2) is allowed. If the last argument is a boolean,
  then the source objects properties are force copied over to dest.