How to implement "select all/none" option in multi-select?

[vincerubinetti]

What do you think the appropriate way is to do something like this:

I could put a button element above the other options, but then keyboard-only users would not be able to access it. Maybe a "select/deselect" all functionality should be built-in?

[segunadebayo]

Closing as outdated — please refer to the updated v1.0 documentation for current API patterns.