code: function() {
      this.jsonInit({
        "message0": Blockly.Msg.LOOKS_BACKDROPNUMBERNAME,
        "args0": [
          {
            "type": "field_dropdown",
            "name": "NUMBER_NAME",
            "options": [
              [Blockly.Msg.LOOKS_NUMBERNAME_NUMBER, 'number'],
              [Blockly.Msg.LOOKS_NUMBERNAME_NAME, 'name']
            ]
          }
        ],
        "category": Blockly.Categories.looks,
        "checkboxInFlyout": true,
        "extensions": ["colours_looks", "output_number"]
      });
    }
docs: Block to report backdrop's number or name
  @this Blockly.Block