6.15: Dropdowns Visibility Events example
=========================================
**Primary Actor**: User

**Scope**: Ngx-bootstrap DEMO / BS version 3&4

**Goal**: Show user example how to subscribe to dropdown visibility events

Main success scenario:
----------------------
1. User opens Dropdowns demo page
2. User clicks on Visibility Events sub-menu
3. User see clickable button "Button dropdown"
4. When user clicks on "Button dropdown", then dropdown opened and there are 3 items and card "Event onShown is fired" should be shown
5. When user clicks on any item, then dropdown closed and card "Event onHidden is fired" is shown
6. When user clicks on "Button dropdown" again, then dropdown opened and card "Event onHidden is fired" is hidden
7. When user clicks on any item, then dropdown closed and card "Event onHidden is fired" is shown again

Variations:
-----------
2*. User scroll to Visibility Events sub-menu