I wrote a spell checker for my undergraduate to help with automation research back in 2011, it allowed the researcher to do things like insert words that would

I wrote a spell checker for my undergraduate to help with automation research back in 2011, it allowed the researcher to do things like insert words that would show as incorrect when they were actually correct, and see if people would notice with varying levels of difficulty. The idea was to try to measure how some automated systems can improve or reduce net performance. I actively tried to avoid using libraries, and ended up writing most of it in vanilla JavaScript - including a bunch of DOM manipulations, which was suicide at the time. I even wrote my own XML-based DSL for defining the input text. Would have loved to actually follow through with the research but phd's don't pay bills.