Double Vision

One of the things that is supposed to be avoided in writing, and spellcheckers freak out over all the time, is words written twice. The obvious reason for this is of course detecting against mistakes, especially constant double words at the line break that are almost completely unnoticeable except if paying careful attention. A word on the end of a line, and the same word at the beginning of the next line. I know I've found many occurrences in well proofread media where double words have slipped through the cracks.

The problem with English, however, which I end up hitting a lot, is when I do it on purpose, something which as I mentioned, should be avoided. I use it to form my sentence because that is the natural flow of my writing, specifically because the words have two different meanings. Particularly in two cases: "that that", and "on on". Their actual use is reversible in the sentence, but can happen together. In the case of the "that that", one would be a conjugation, and the other a reference of object, such as in "Did I mention that that is a type of cheese?" In the case of the "on on" one is used as a location, and the other is used as a state, most often referring to a light, such as in "The indicator light is on on the dashboard." Actual valid uses because they are in this case two different words, but because of the complexity of English it looks wrong to the spellchecker so it just outright reports it as incorrect.