Serialize textbox element.

def serialize_textbox(ctx, document, txtbox, root):
    """Serialize textbox element."""

    _div = etree.SubElement(root, 'div')
    _div.set('class', 'textbox')

    for elem in txtbox.elements:
        _ser = ctx.get_serializer(elem)

        if _ser:
            _ser(ctx, document, elem, _div)

    fire_hooks(ctx, document, txtbox, _div, ctx.get_hook('textbox'))

    return root