What constitues as visible though? There is the obvious non-visible CSS modifiers like display: hidden; - but at what point does an off screen rendered text act

What constitues as visible though? There is the obvious non-visible CSS modifiers like display: hidden; - but at what point does an off screen rendered text actually count as hidden? If you were wanting to copy the entire contents of a page, and the browser assumed anything off screen was invisible then you would not be able to copy everything at once when it goes below the fold. Different screen resolutions and devices would cause other issues there as well.