Feature request usability: filter by multiselection

[ChristianMayer]

When I select a tag in the list on the bottom right this tag is immediately used as a filter on the image list on the left side. This is great.
But when I select multiple entries only the last one is used for the list on the left.

My expectation was that this multiselection is creating a filter where the entries are either ANDed or ORed together. I.e. the union or the intersection of the selection is shown. Both are valid expectations.

So my feature request is:

1. The multiple tags are selected all of them should be used in the filter (it's your decision whether that means AND or OR)
2. Enhancement to 1.: depending on the press of a modifier key like "alt" an additionally selected tag is added to the filter in the opposite fashion. (E.g. normally all tags are ANDed, then a alt+click would add that tag with an OR)