The HTTP Pragma header has different effects that are implementation-specific and is not included in the HTTP specification. However, it can be used for backward compatibility with HTTP/1.0 caches that do not have a HTTP Cache-Control HTTP/1.1 header.
The Pragma header is implementation-specific and is not part of the HTTP specification. However, its behavior is semantically equivalent to HTTP
Cache-Control: no-cache if the Cache-Control header field is omitted in an HTTP/1.0 request.
The only directive is