def grid_auto(tokens):
    """``grid-auto-columns`` and ``grid-auto-rows`` properties validation."""
    return_tokens = []
    for token in tokens:
        track_size = _track_size(token)
        if track_size:
            return_tokens.append(track_size)
            continue
        return
    return tuple(return_tokens)
``grid-auto-columns`` and ``grid-auto-rows`` properties validation.
weasyprint/css/validation/properties.py