code: function NumberField(type, options) {
    Field.call(this, type, options);
    this.arg = new Argument();
  
    this.element = util.createElement(this.document, 'input');
    this.element.type = 'number';
    if (this.type.max) {
      this.element.max = this.type.max;
    }
    if (this.type.min) {
      this.element.min = this.type.min;
    }
    if (this.type.step) {
      this.element.step = this.type.step;
    }
  
    this.onInputChange = this.onInputChange.bind(this);
    this.element.addEventListener('keyup', this.onInputChange, false);
  
    this.onFieldChange = util.createEvent('NumberField.onFieldChange');
  }
docs: A field that allows editing of numbers using an [input type=number] field