The HTTP If-None-Match request header makes a request conditional.
The server returns the requested resource in GET and HEAD methods with a 200 status, only if it doesn't have an ETag matching the ones in the If-None-Match header.
For other methods, the request will be processed only if the eventually existing resource's ETag doesn't match any of the values listed....The HTTP If-None-Match request header makes a request conditional.
The server returns the requested resource in GET and HEAD methods with a 200 status, only if it doesn't have an ETag matching the ones in the If-None-Match header.
For other methods, the request will be processed only if the eventually existing resource's ETag doesn't match any of the values listed.