code: function() {
      this.setColour(Blockly.Blocks.texts.HUE);
      this.appendDummyInput()
          .appendField(Blockly.Msg.TEXT_CREATE_JOIN_TITLE_JOIN);
      this.appendStatementInput('STACK');
      this.setTooltip(Blockly.Msg.TEXT_CREATE_JOIN_TOOLTIP);
      this.contextMenu = false;
    }
docs: Mutator block for container.
  @this Blockly.Block