    def is_monolithic(self):
        """Return whether this box is monolithic."""
        # https://www.w3.org/TR/css-break-3/#monolithic
        return (
            isinstance(self, AtomicInlineLevelBox) or
            isinstance(self, ReplacedBox) or
            self.style['overflow'] in ('auto', 'scroll') or
            (self.style['overflow'] == 'hidden' and
             self.style['height'] != 'auto'))
Return whether this box is monolithic.
weasyprint/formatting_structure/boxes.py