The UX of keyword searches

I'm not interested in the UI of search boxes and results, but the behaviour of a keyword search. Features like stemming, synonyms, disambiguation, typo correction etc. What makes a great experience for the process of typing in a query and receiving some relevant results?

I realise this is a broad question, but when researching online I'm struggling to find studies or guidance on these aspects of the search experience, as opposed to what the search box should look like, and how the results are presented.