code: function() {
      this.jsonInit({
        "message0": Blockly.Msg.CONTROLS_FOR_TITLE,
        "args0": [
          {
            "type": "field_variable",
            "name": "VAR",
            "variable": null
          },
          {
            "type": "input_value",
            "name": "FROM",
            "check": "Number",
            "align": "RIGHT"
          },
          {
            "type": "input_value",
            "name": "TO",
            "check": "Number",
            "align": "RIGHT"
          },
          {
            "type": "input_value",
            "name": "BY",
            "check": "Number",
            "align": "RIGHT"
          }
        ],
        "inputsInline": true,
        "previousStatement": null,
        "nextStatement": null,
        "colour": Blockly.Blocks.loops.HUE,
        "helpUrl": Blockly.Msg.CONTROLS_FOR_HELPURL
      });
      this.appendStatementInput('DO')
          .appendField(Blockly.Msg.CONTROLS_FOR_INPUT_DO);
      // Assign 'this' to a variable for use in the tooltip closure below.
      var thisBlock = this;
      this.setTooltip(function() {
        return Blockly.Msg.CONTROLS_FOR_TOOLTIP.replace('%1',
            thisBlock.getFieldValue('VAR'));
      });
    }
docs: Block for 'for' loop.
  @this Blockly.Block