The paratext is everything in a book or manuscript that’s not the author’s words: illustrations, footnotes, font and layout, quality of materials, the size or shape of the pages. The way a text is presented visually can strongly affect or even change the way we read and understand that text.
What kind of container is it in?
Is it in the salad bar?
Is it on a steam table?
Is a line forming to get it?
Another way of thinking of this is the distinction between form and content. If content is the text itself, form is the paratext—how that content is made visible to you.
The paratext can help you determine whether a particular text is useful to you. If you decide it’s not useful, see if looking at the text from a different angle can help you. If not, stop reading and find another text.