Without multi-selection, browser sub-app is barely usable in many cases. We need to support it this or that way:

• proposed solution is to generalise the ValueContext, so that instead of a single value it would operate over the ValueModel or something (such model would provide convenient API for distinguishing between single/multi-value, allow to stream the selected items etc)
• another possible solution is to treat any value selection as a multi-selection. This seems like an easy solution but might drag some inconveniences along (usability of such API and solutions built around it might look not that fancy).