I did some research and don't see any restriction on nested pre tags, yet
Soup includes <pre> in "NonNestableBlockTagsForHtml". This causes the
following to be parsed as two sibling <pre> tags:
This act shall take effect immediately.
Moving <pre> from NonNestableBlockTagsForHtml to NestableBlockTagsForHtml
seems to be The Right Thing To Do. Any objection (I'm certainly not an HTML
expert). If not, I'll commit to my GH fork and feel free to merge back to
StHub or wherever.