def break_before_after(keyword):
    """``break-before`` and ``break-after`` properties validation."""
    return keyword in ('auto', 'avoid', 'avoid-page', 'page', 'left', 'right',
                       'recto', 'verso', 'avoid-column', 'column', 'always')
``break-before`` and ``break-after`` properties validation.
weasyprint/css/validation/properties.py