!!! Overview
[{$pagename}] are defined in [RFC 7234] section-5.5 The "Warning" [HTTP Header Field] is used to carry additional information about the status or transformation of a message that might not be reflected in the [HTTP Status Code].  

[{$pagename}] information is typically used to warn about possible incorrectness introduced by caching operations or transformations applied to the payload of the message.

[Warnings] can be used for other purposes, both [cache]-related and otherwise.  The use of a [warning], rather than an [error] [HTTP Status Code], distinguishes these responses from true failures. Warning header fields can in general be applied to any [message], however some [{$pagename}] are specific to [Cache-Control] and can only be applied to [HTTP Response] messages.

[HTTP Header Field] [{$pagename}]s are defined in an [IANA Registry] [Hypertext Transfer Protocol [HTTP Warn Codes|https://www.iana.org/assignments/http-warn-codes/http-warn-codes.xhtml|target='_blank']

%%zebra-table
%%sortable
%%table-filter
||code||Type||Status text||Description||Reference
|[110|HTTP Warning 110]|[Warning]|Response is Stale|A [cache] [SHOULD] generate this whenever the sent response is stale.|[RFC 7234]
|[111|HTTP Warning 111]|[Warning]|Revalidation Failed|A [cache] [SHOULD] generate this when sending a stale response because an attempt to validate the response failed, due to an inability to reach the server.|[RFC 7234]
|[112|HTTP Warning 112]|[Warning]|Disconnected Operation|A [cache] [SHOULD] generate this if it is intentionally disconnected from the rest of the [network] for a period of time.|[RFC 7234]
|[113|HTTP Warning 113]|[Warning]|Heuristic Expiration|A [cache] [SHOULD] generate this if it heuristically chose a freshness [lifetime] greater than 24 hours and the response's age is greater than 24 hours.|[RFC 7234]
|[199|HTTP Warning 199]|[Warning]|Miscellaneous Warning|The warning text can include arbitrary information to be presented to a human user or logged. A system receiving this warning [MUST NOT] take any automated action, besides presenting the warning to the user.|[RFC 7234]
|[214|HTTP Warning 214]|[Warning]|Transformation Applied|This [Warning] code [MUST] be added by a [proxy] if it applies any transformation to the representation, such as changing the [content-coding], [media-type], or modifying the representation [data], unless this [{$pagename}] already appears in the response.|[RFC 7234]
|[299|HTTP Warning 299]|[Warning]|The warning text can include arbitrary information to be presented to a [Human] user or logged. A system receiving this warning [MUST NOT] take any automated action.|[RFC 7234]
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!! More Information
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