!!! Overview
[{$pagename}] is a [HTTP Response Header] that indicates how long the [User-agent] [SHOULD] wait before making a follow-up request. 

There are three main cases this header is used:
* When sent with a [HTTP 503] ([Service Unavailable]) response, this indicates how long the service is expected to be unavailable.
* When sent with a [HTTP 429] ([Too Many Requests]) response, this indicates how long to wait before making a new request.
* When sent with a [URL redirection] response, such as [HTTP 301] ([Moved Permanently]), this indicates the minimum time that the [User-agent] is asked to wait before issuing the redirected request.

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [Retry-After|https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After|target='_blank'] - based on information obtained 2018-03-14-