Preprocessing methods besides stop words, regular expressions, lemmatization and stemming

Hi everyone!

I'm doing a NLP classification problem for university. In it, we are asked to use the methods listed in the title, but also "extra methods" for some small extra points.

The labs professor wasn't really able to name some when I asked for help, and searching online is not helping either. The professor seemed a bit unsure if they will keep this requirement, but in case they do:

Does anyone know of any other preprocessing methods that ccan …

classification labs languagetechnology lemmatization nlp professor searching small stemming university words