Hi
I don't see anything for auto complete to restrict within collections as Search and Promote only storing the list words while doing index based on the fields we asked to index.
![Screen Shot 2020-05-21 at 9.20.32 AM.png Screen Shot 2020-05-21 at 9.20.32 AM.png](https://experienceleaguecommunities.adobe.com/t5/image/serverpage/image-id/24141i8AB9C080A14ED63F/image-size/medium/is-moderation-mode/true?v=v2&px=400)
And in the response it is returning only the words and I think filtering is not possible
acObj.generateRequest = function(q) {return "?query=" + q + "&max_results=" + acObj.maxResultsDisplayed + "&beginning=1";};
You can check below link to see which has details of customizing auto-complete results.
https://yui.github.io/yui2/docs/yui_2.9.0_full/autocomplete/
Hope this helps !