code: private void _warn (@Nonnull final IPSElement aSourceElement, @Nonnull final String sMessage)
    {
      ValueEnforcer.notNull (aSourceElement, "SourceElement");
      ValueEnforcer.notNull (sMessage, "Message");
  
      m_aErrorHandler.warn (m_aResource, aSourceElement, sMessage);
    }
docs: Emit a warning with the registered error handler.
  
  @param aSourceElement
  The source element where the error occurred.
  @param sMessage
  The main warning message.