docs: def specifiedColumns(self):
          """
          Returns the list of columns that are specified based on the column
          view for this widget.
          
          :return     [<orb.Column>, ..]
          """
          columns = []
          table = self.tableType()
          tree = self.treePopupWidget()
          schema = table.schema()
          
          if self._specifiedColumns is not None:
              colnames = self._specifiedColumns
          else:
              colnames = tree.columns()
          
          for colname in colnames:
              if isinstance(colname, Column):
                  columns.append(colname)
              else:
                  col = schema.column(colname)
                  if col and not col.isProxy():
                      columns.append(col)
          
          return columns