def to_xml_name(name):
    """Convert field name to tag-like name as used in QuickBase XML.

    >>> to_xml_name('This is a Field')
    'this_is_a_field'
    >>> to_xml_name('800 Number')
    '_800_number'
    >>> to_xml_name('A & B')
    'a___b'
    >>> to_xml_name('# of Whatevers')
    '___of_whatevers'

    """
    xml_name = ''.join((ch if ch.isalnum() else '_') for ch in name.lower())
    if not xml_name[0].isalpha():
        xml_name = '_' + xml_name
    return xml_name