def font_variation_settings(tokens):
    """``font-variation-settings`` property validation."""
    if len(tokens) == 1 and get_keyword(tokens[0]) == 'normal':
        return 'normal'

    @comma_separated_list
    def font_variation_settings_list(tokens):
        if len(tokens) == 2:
            key, value = tokens
            if key.type == 'string' and value.type == 'number':
                return key.value, value.value

    return font_variation_settings_list(tokens)
``font-variation-settings`` property validation.
weasyprint/css/validation/properties.py