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An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this specification SHOULD use an HTTP-Version of  "HTTP/1.1" in their messages, and MUST do so for any message that is  not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values, see RFC 2145 [36].

An HTTP client SHOULD send a request version equal to the highest version for which the client is at least conditionally compliant, and  whose major version is no higher than the highest version supported by the server, if this is known.  An HTTP client MUST NOT send a version for which it is not at least conditionally compliant.

An HTTP client MAY send a lower request version, if it is known that the server incorrectly implements the HTTP specification, but only after the client has determined that the server is actually buggy.

An HTTP server SHOULD send a response version equal to the highest version for which the server is at least conditionally compliant, and whose major version is less than or equal to the one received in the request.  An HTTP server MUST NOT send a version for which it is not at least conditionally compliant.  A server MAY send a 505 (HTTP Version Not Supported) response if cannot send a response using the major version used in the client's request.

An HTTP server MAY send a lower response version, if it is known or suspected that the client incorrectly implements the HTTP specification, but this should not be the default, and this SHOULD NOT be done if the request version is HTTP/1.1 or greater.

An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this specification SHOULD use an HTTP-Version of  "HTTP/1.1" in their messages, and MUST do so for any message that is  not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values, see RFC 2145 [36].

An HTTP client SHOULD send a request version equal to the highest version for which the client is at least conditionally compliant, and  whose major version is no higher than the highest version supported by the server, if this is known.  An HTTP client MUST NOT send a version for which it is not at least conditionally compliant.

An HTTP client MAY send a lower request version, if it is known that the server incorrectly implements the HTTP specification, but only after the client has determined that the server is actually buggy.

An HTTP server SHOULD send a response version equal to the highest version for which the server is at least conditionally compliant, and whose major version is less than or equal to the one received in the request.  An HTTP server MUST NOT send a version for which it is not at least conditionally compliant.  A server MAY send a 505 (HTTP Version Not Supported) response if cannot send a response using the major version used in the client's request.

An HTTP server MAY send a lower response version, if it is known or suspected that the client incorrectly implements the HTTP specification, but this should not be the default, and this SHOULD NOT be done if the request version is HTTP/1.1 or greater.

An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this specification SHOULD use an HTTP-Version of  "HTTP/1.1" in their messages, and MUST do so for any message that is  not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values, see RFC 2145 [36].