code: public void error(SourceLocator srcLctr, String msg, Exception e) throws TransformerException
    {
      error(srcLctr, msg, null, e);
    }
docs: Tell the user of an error, and probably throw an
  exception.
  
  @param msg Message text to issue
  @param e Exception to throw
  @throws XSLProcessorException thrown if the active ProblemListener and XPathContext decide
  the error condition is severe enough to halt processing.
  
  @throws TransformerException
  @xsl.usage internal