def font_variant(tokens):
    """``font-variant`` descriptor validation."""
    if len(tokens) == 1:
        keyword = get_keyword(tokens[0])
        if keyword in ('normal', 'none', 'inherit'):
            return []
    values = []
    for name, sub_tokens in expand_font_variant(tokens):
        try:
            values.append(properties.validate_non_shorthand(
                sub_tokens, f'font-variant{name}', required=True))
        except InvalidValues:
            return None
    return values
``font-variant`` descriptor validation.
weasyprint/css/validation/descriptors.py