[throwaway290]

It's slightly individual, e.g. some may pick up on misspellings in books (or anachronisms or mismatching sound in video) more easily than others, but my theory is whenever something concerns the story or requires any effort to determine whether it concerns the story or not it breaks immersion.

Misspellings in books, foreign objects or people in a show or film, obviously fake phone numbers and things like that fall into that category.

On the other hand, things like paper quality or font choice (and lens angles, cuts, video resolution, color) tend to not break immersion if the story is right.