code: public void defineFrom(InputProblemReporter rep, DTDElement definedElem,
                             boolean fullyValidate)
          throws XMLStreamException
      {
          if (fullyValidate) {
              verifyUndefined();
          }
          mValidator = definedElem.mValidator;
          mAllowedContent = definedElem.mAllowedContent;
          mergeMissingAttributesFrom(rep, definedElem, fullyValidate);
      }
docs: Method called to "upgrade" a placeholder using a defined element,
  including adding attributes.