Create a KML Folder element.

    Args:
      parent: The parent ElementTree.Element instance.
      name: The folder name as a string.
      visible: Whether the folder is initially visible or not.
      description: A description string or None.

    Returns:
      The folder ElementTree.Element instance.

def _CreateFolder(self, parent, name, visible=True, description=None):
    """Create a KML Folder element.

    Args:
      parent: The parent ElementTree.Element instance.
      name: The folder name as a string.
      visible: Whether the folder is initially visible or not.
      description: A description string or None.

    Returns:
      The folder ElementTree.Element instance.
    """
    folder = ET.SubElement(parent, 'Folder')
    name_tag = ET.SubElement(folder, 'name')
    name_tag.text = name
    if description is not None:
      desc_tag = ET.SubElement(folder, 'description')
      desc_tag.text = description
    if not visible:
      visibility = ET.SubElement(folder, 'visibility')
      visibility.text = '0'
    return folder