Event message for 'capabilities' event type. The event indicates that one or more capabilities have changed. Since the capabilities are dependent on the frontend and its UI, it might not be possible to change that at random times (or too late). Consequently this event has a hint characteristic: a frontend can only be expected to make a 'best effort' in honouring individual capabilities but there are no guarantees. Only changed capabilities need to be included, all other capabilities keep their values.

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