Invisible Formatting

Me too, xkcd.com/2109

A web comic by XKCD, the caption at the bottom reads "when editing text, in the back of my mind I always worry that I'm adding invisible formatting that will somehow cause a problem in the distant future". The comic shows the word 'not' being selected in a sentence, then turned into bold, and then the bold being removed again. The final panel reveals the fear that the bold was not removed from the space after the word 'not'