!!! Overview
[{$pagename}]s are defined in [RFC 7232] and several [HTTP Header Fields] are called conditional headers, lead to [{$pagename}]. 

These are:
* If-Match - Succeeds if the [Etag] of the distant [resource] is equal to one listed in this header. By default, unless the [etag] is prefixed with 'W/', it performs a strong validation.
* If-None-Match - Succeeds if the [Etag] of the distant resource is different to each listed in this header. By default, unless the [etag] is prefixed with 'W/', it performs a strong validation.
* If-Modified-Since - Succeeds if the Last-Modified [date] of the distant [resource] is more recent than the one given in this header.
* If-Unmodified-Since - Succeeds if the Last-Modified [date] of the distant resource is older or the same than the one given in this header.
* If-Range - Similar to If-Match, or If-Unmodified-Since, but can have only one single etag, or one [date]. If it fails, the range request fails, and instead of a [HTTP 206] Partial Content response, a [HTTP 200] OK is sent with the complete [resource].


!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [HTTP conditional requests|https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditional_requests|target='_blank'] - based on information obtained 2018-08-01-