I've been in the preview for a bit.

1) This doesn't seem to exist in quite that way, but you can prefix a literal with "def:" and the engine will return only definitions of that thing (so far as it can tell). It's not quite what you (or I!) want, but close.

2) This exists and is called "scopes". On the landing page, to the left of the search bar, click the grey pill that says "All repos". At the bottom there is a "custom scopes" option.