Hi Bruce,
Thanks for all the details!
By “documents” do you mean files, such as PDF etc..? If yes, then I assume you mean when clicking on the document result itself the text should be highlighted? Unfortunately that is not possible. When a document is opened within the browser, it is opened within it’s own sandbox environment (not within wordpress), so there is no way to add scripts to it to highlight.
Google chrome will have a neat little feature in the future, where setting a query argument will hihglight some text, similarly to their search in file feature (CTRL+F). Once that’s possible we will try to integrate with that, but I don’t know how usable it’s going to be.