the search tools filters are displayed (or hidden) using the filter options button. This uses the searchtools.js script.

There is no accessible indicator if the search tools are being displayed or not. All you can do is to select the button and then keep tabbing to see if any filters appeared. If the search tools were already displayed then you just closed them and you have to tab backwards and select the button again and then keep tabbing until you reach the buttons.

The filters should be the next item in the navigation order when they are expanded

1. the button should have aria-expanded=true/false so that you know the current state.
2. if you select the button to expand/display the filters then the next tab should take you to the first filter. and not the sort order

cosmetically it would be nice if the expand/collapse was smoothly animated (as you see when you use the bootstrap collapse for example)