code: @Override
      public void error( F0<String> msg )
      {
          if ( compilerLogger.isErrorEnabled() )
          {
              String msgString = msg.apply();
              errors.append( msgString ).append( '\n' );
              compilerLogger.error( msgString );
          }
      }
docs: Send a message to the user in the <b>error</b> error level
  if the <b>error</b> error level is enabled.
  
  @param msg message