A server generates an entity tag from a timestamp with one-second resolution, so the representation can change twice within one tick. What does RFC 9110 require of the ETag it sends?
It MAY be sent unmarked, since entity tags are opaque to clients
It MUST NOT be sent at all; only Last-Modified is permitted in that case
It MUST be marked weak by prefixing the opaque value with W/✓الإجابة الصحيحة
It MUST be marked weak, and clients MUST then use it only with If-Modified-Since
الشرح
Strong is the default for an entity tag, so a generator that cannot meet the strong-validator characteristics is required to mark the tag with the case-sensitive W/ prefix. Weak tags remain usable in If-None-Match, which compares weakly; what they cannot be used for is If-Range.