code: function() {
      this.appendDummyInput()
          .appendField(Blockly.Msg.PROCEDURES_MUTATORCONTAINER_TITLE);
      this.appendStatementInput('STACK');
      this.appendDummyInput('STATEMENT_INPUT')
          .appendField(Blockly.Msg.PROCEDURES_ALLOW_STATEMENTS)
          .appendField(new Blockly.FieldCheckbox('TRUE'), 'STATEMENTS');
      this.setColour(Blockly.Blocks.procedures.HUE);
      this.setTooltip(Blockly.Msg.PROCEDURES_MUTATORCONTAINER_TOOLTIP);
      this.contextMenu = false;
    }
docs: Mutator block for procedure container.
  @this Blockly.Block