What if instead of a sidebar, you could get information about a word by putting your mouse over it and doing something? (does javascript let you trap rightclicks?)

The nice thing about a sidebar is you can investigate a broader scope of the document's semantic content, as opposed to just specific sections. (but yes, it does... and this might be a good way to narrow the context)

Yes, it let's you trap right clicks. The event is called "contextmenu".