How is the filling of the address in the Yandex map input implemented?

Question

JavaScript

Good afternoon! I've been struggling with a banal task for 2 days now.
Here is an example of a site - a site



It turns out that the choice of the address goes only for one city? How did they implement it?
Is the search carried out in the green zone?
I tried to limit the zone in this way, but some kind of strange algorithm, other cities still slip through.

suggestView = new ymaps.SuggestView('suggest', {
                            boundedBy: [
                                [
                                    59.633711,
                                    29.425117
                                ],
                                [
                                    60.244813,
                                    30.759528
                                ] // cпб
                            ]
                        }),

Answer 1

Read here .
You need the boundedBy
upd parameter.
Add your provider, in which you will add the desired city at the beginning of the search query Like this (there is a limit for Moscow):

Answer 2

Firstly, you can always look at "how they implemented it", this is the js code available to everyone. I'm already silent, for the lazy, look at the outgoing requests.
Secondly, who is stopping you from filtering the received data from "other cities are skipping".