Support 'selects="multiple"'

[Westbrook]

Expected Behaviour

The Picker interface is able to leverage the underlying sp-menu selects="multiple" functionality and deliver it visually to a visitor.

Actual Behaviour

multiple has been left out of #1661 for scope control.

[adixon-adobe]

I'd expect selected='multiple' to be simpler to handle in ActionMenu since the selected state doesn't update when a selection is made. My understanding last we talked to design was that Picker is really designed for single selection, so for the actual control (not PickerBase), I don't think we'd need to add this support unless there's a strong proposal made for why it's needed. I'm guessing SplitButton is similar.

[Westbrook]

Yes.

• sp-action-menu, kind of a no brainer, just wanted to leave it out for this first pass for the accessibility questions in sp-picker.
• sp-picker, can support it, but needs design direction. Is it just Value 1, Value 2, etc. or something more. I think it's fine to add, but with caveats and a little extra love around what we do to accessibly surface that data for screen readers.
• sp-split-button, I'm not sure it should ever be multiple. You either get no selection with type="more" or you get a selection by default...could be convinced if you saw a better path forward there.

[TarunAdobe]

I talked a bunch of designers in AD-Design team and asked them if some product is using a similar component and so far everyone wants either a combobox pattern or a tagfield pattern. Not sure if having selects='multiple' makes sense in a picker. Need a solid usecase before moving forward with this idea