def _line_names(arg):
    """Parse ``line-names``."""
    return_line_names = []
    if arg.type == '[] block':
        for token in arg.content:
            if token.type == 'ident':
                return_line_names.append(token.value)
            elif token.type != 'whitespace':
                return
        return tuple(return_line_names)
Parse ``line-names``.
weasyprint/css/validation/properties.py