Perhaps for some odd reason you have never looked at a modern edition of an ancient or medieval text—whether in Latin, Greek, Hebrew, Old Norse, Sanskrit, Old High German, or whatever. In that case, it’s not too late to start!
If, on the other hand, you have looked at such a text, you may wonder (as I did) what all that gibberish down below in the footnotes really means. Most likely, you will (as I did) just ignore it. Classicist Peter Gainsford, however, argues convincingly that this isn’t gibberish, that in fact the “app crit” is your best friend. So watch Gainsford’s excellent video below, and then, if you’re interested, read his blog post. You’ll learn a lot (as I did).