code: function() {
      this.jsonInit({
        "message0": Blockly.Msg.LOOKS_GOTOFRONTBACK,
        "args0": [
          {
            "type": "field_dropdown",
            "name": "FRONT_BACK",
            "options": [
              [Blockly.Msg.LOOKS_GOTOFRONTBACK_FRONT, 'front'],
              [Blockly.Msg.LOOKS_GOTOFRONTBACK_BACK, 'back']
            ]
          }
        ],
        "category": Blockly.Categories.looks,
        "extensions": ["colours_looks", "shape_statement"]
      });
    }
docs: "Go to front/back" Block.
  @this Blockly.Block