Specify namespaces for tags
Specify namespaces for tags

This is a proposition for closing #931.

This should be a fairly uncontroversial addition (apart from bike-shedding), which only defines behavior for clients that want use tags or expose tagging functionality to their users.

The idea of adding this to the spec is to ensure clients can peacefully share the tag namespace without conflicting with each other, using rules similar to namespaces for state keys.
matrix-org/matrix-doc,matrix-org/matrix-doc,matrix-org/matrix-doc,matrix-org/matrix-doc