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Note that this won't prevent the page from being displayed in other sizes, where it will most likely have a broken layout instead.

True, but with CSS you define one layout for the web format alongside a different layout for the print format, using the @page rule.

If I want only the print format this will require double the effort though.

No it doesn't? If you only want the print format, just do the print format layout, ignore the web format. Why do you care that it's broken there?