!!! Overview [1] [2]
[{$pagename}] is a [HTTP Entity Header] ([HTTP Header Field]) that indicates the [media-type] of the [HTTP Body].

[{$pagename}] in the case of the [HTTP HEAD] method, the [media-type] that would have been sent had the [HTTP Request] been a [HTTP GET].

In [HTTP Responses], a [{$pagename}] [HTTP Entity Header] tells the [client] what the [media-type] of the returned content actually is. [Browsers] [MAY] do [MIME] sniffing in some cases and will __not__ necessarily follow the value of the [{$pagename}]; to prevent this behavior, the header [X-Content-Type-Options] can be set to nosniff.

In [HTTP Requests], (such as [HTTP POST] or [HTTP PUT]), the [client] tells the [server] what [media-type] of [HTTP Body] is being sent.

%%prettify 
{{{
Content-Type   = "Content-Type" ":" media-type
}}} /%

Media types are defined in section 3.7. An example of the field is
%%prettify 
{{{
Content-Type: text/html; charset=ISO-8859-4
}}} /%

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
----
* [#1] - [14.17 Content-Type|https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.17/|target='_blank'] - based on information obtained 2016-06-25- 
* [#2] - [Content-Type|https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Type|target='_blank'] - based on information obtained 2017-07-12