code: function () {
                  var value;
  
                  if (! $re(/^\(opacity=/i)) { return; }
                  value = $re(/^\d+/) || this.entities.variable();
                  if (value) {
                      expectChar(')');
                      return new(tree.Alpha)(value);
                  }
              }
docs: IE's alpha function  alpha(opacity=88)