code: function() {
      this.jsonInit({
        "message0": "%1",
        "args0": [
          {
            "type": "field_dropdown",
            "name": "KEY_OPTION",
            "options": [
              [Blockly.Msg.EVENT_WHENKEYPRESSED_SPACE, 'space'],
              [Blockly.Msg.EVENT_WHENKEYPRESSED_UP, 'up arrow'],
              [Blockly.Msg.EVENT_WHENKEYPRESSED_DOWN, 'down arrow'],
              [Blockly.Msg.EVENT_WHENKEYPRESSED_RIGHT, 'right arrow'],
              [Blockly.Msg.EVENT_WHENKEYPRESSED_LEFT, 'left arrow'],
              [Blockly.Msg.EVENT_WHENKEYPRESSED_ANY, 'any'],
              ['a', 'a'],
              ['b', 'b'],
              ['c', 'c'],
              ['d', 'd'],
              ['e', 'e'],
              ['f', 'f'],
              ['g', 'g'],
              ['h', 'h'],
              ['i', 'i'],
              ['j', 'j'],
              ['k', 'k'],
              ['l', 'l'],
              ['m', 'm'],
              ['n', 'n'],
              ['o', 'o'],
              ['p', 'p'],
              ['q', 'q'],
              ['r', 'r'],
              ['s', 's'],
              ['t', 't'],
              ['u', 'u'],
              ['v', 'v'],
              ['w', 'w'],
              ['x', 'x'],
              ['y', 'y'],
              ['z', 'z'],
              ['0', '0'],
              ['1', '1'],
              ['2', '2'],
              ['3', '3'],
              ['4', '4'],
              ['5', '5'],
              ['6', '6'],
              ['7', '7'],
              ['8', '8'],
              ['9', '9']
            ]
          }
        ],
        "extensions": ["colours_sensing", "output_string"]
      });
    }
docs: Options for Keys
  @this Blockly.Block