docs: def register(self, plugin, columnType=None, columnName=None):
          """
          Registers a plugin to handle particular column types and column names
          based on user selection.
          
          :param      plugin     | <XOrbQueryPlugin>
                      columnType | <orb.ColumnType> || None
                      columnName | <str> || None
          """
          self._plugins[(columnType, columnName)] = plugin