Return an instance of |Table| appropriate to *tag*, loaded from
    *font_file* with content of *length* starting at *offset*.

def _TableFactory(tag, stream, offset, length):
    """
    Return an instance of |Table| appropriate to *tag*, loaded from
    *font_file* with content of *length* starting at *offset*.
    """
    TableClass = {
        'head': _HeadTable,
        'name': _NameTable,
    }.get(tag, _BaseTable)
    return TableClass(tag, stream, offset, length)