如何使用wtforms设置复选框标签的类别？

from wtforms import fields, widgets

class CustomCheckboxField(fields.Field):
    widget = widgets.CheckboxInput()

    def __init__(self, label=None, validators=None, **kwargs):
        super(CustomCheckboxField, self).__init__(label, validators, **kwargs)

    def pre_validate(self, form):
        # 验证字段的值
        if self.data:
            # 执行相应的验证操作
            pass

class MyForm(FlaskForm):
    categories = CustomCheckboxField('Categories')

@app.route('/', methods=['GET', 'POST'])
def index():
    form = MyForm()
    if form.validate_on_submit():
        # 处理表单提交
        pass
    return render_template('index.html', form=form)

<form method="POST" action="/">
  {{ form.hidden_tag() }}
  {{ form.categories.label }}
  {{ form.categories() }}
  <input type="submit" value="Submit">
</form>