def _fixed_size(token):
    """Parse ``fixed-size``."""
    length = get_length(token, negative=False, percentage=True)
    if length:
        return length
    function = parse_function(token)
    if function:
        name, args = function
        if name == 'minmax' and len(args) == 2:
            length = get_length(args[0], negative=False, percentage=True)
            if length:
                track_breadth = _track_breadth(args[1])
                if track_breadth:
                    return ('minmax()', length, track_breadth)
            keyword = get_keyword(args[0])
            if keyword in ('min-content', 'max-content', 'auto') or length:
                fixed_breadth = get_length(
                    args[1], negative=False, percentage=True)
                if fixed_breadth:
                    return ('minmax()', length or keyword, fixed_breadth)
Parse ``fixed-size``.
weasyprint/css/validation/properties.py