def quotes(tokens):
    """``quotes`` property validation."""
    if len(tokens) == 1:
        if (keyword := get_keyword(tokens[0])) in ('auto', 'none'):
            return keyword
    if (tokens and len(tokens) % 2 == 0 and
            all(token.type == 'string' for token in tokens)):
        strings = tuple(token.value for token in tokens)
        # Separate open and close quotes.
        # eg.  ('«', '»', '“', '”')  -> (('«', '“'), ('»', '”'))
        return strings[::2], strings[1::2]
``quotes`` property validation.
weasyprint/css/validation/properties.py