2.2.6.2.2 must-revalidate
This directive specifies that the cache MUST revalidate that the content is still refreshed before streaming or playing the content. The directive does not apply if caching has been disabled by using the no-cache (section 2.2.6.2.3) directive or the no-user-cache (section 2.2.6.2.5) directive. The must-revalidate directive MUST be ignored by caches that are acting as proxy servers.