docs: def load(self):
          """
          Loads the children for this item.
          """
          if self._loaded:
              return
          
          self.setChildIndicatorPolicy(self.DontShowIndicatorWhenChildless)
          
          self._loaded = True
          column = self.schemaColumn()
          if not column.isReference():
              return
          
          ref = column.referenceModel()
          if not ref:
              return
          
          columns = sorted(ref.schema().columns(),
                           key=lambda x: x.name().strip('_'))
          for column in columns:
              XOrbColumnItem(self, column)