This protocol uses the HTTP Pragma header field to communicate information specific to the operation of the protocol. The Pragma header consists of one or more comma-separated tokens, as specified in [RFC1945] section 10.12.
The following error conditions are treated in an implementation-specific manner:
A Pragma header token which MUST or SHOULD be included by the sender is missing.
A Pragma header token which MUST NOT or SHOULD NOT be included by the sender is received.
A Pragma header token contains incorrect syntax, specifies an invalid value, or contains any other error.<16>