MSC's should always use their unstable prefix when describing event properties or schema.

This prevents implementation bugs where people accidentally assume specific properties are exempt from the namespace rules.

Start by locating the MSC descriptions that discuss event properties or schemas and identify every place where the namespace rule is stated or exceptions are implied. Update the affected specification text so event properties and schemas consistently use the unstable prefix, then review the surrounding MSC references for consistent wording.

Written by the indexing model from the issue text.