!!! Overview
[{$pagename}] is described in [RFC 6454] as "Roughly speaking", two [URIs] are part of the same [{$pagename}] (i.e., represent the same principal) if they have the same [URI Scheme], [hostname], and [port].[{$pagename}] is a concept and both a [Security Consideration] and a [Privacy Consideration] which sets the [Security Domain] and the [Trust] level for the current transaction.

In this [context], "other [origins|Web Origin]" means the [URL] being accessed differs from the location that the JavaScript is running from, by having:
* a different scheme ([HTTP] or [HTTPS])
* a different [DNS Domain] ([hostname])
* a different [port][{$pagename}] is the [HTTP Request Header] "Origin"

The [HTTP Request Header] field has the following syntax: [RFC 6454] section 7.1
* origin              = "Origin:" OWS origin-list-or-null OWS
* origin-list-or-[null] = %x6E %x75 %x6C %x6C / origin-list
* origin-list         = serialized-origin *( SP serialized-origin )
* serialized-origin   = scheme "://" host [[ ":" port ]  ; <[scheme|URI Schemes]>, <[host]>, <[port]> from [RFC 3986]

[{$pagename}] is used in the [Fetch API] as defined by [WHATWG] 

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [RFC 6454|https://tools.ietf.org/html/rfc6454|target='_blank'] - based on information obtained 2017-04-23
* [#2] - [7.5 Origin|https://html.spec.whatwg.org/multipage/origin.html|target='_blank'] - based on information obtained 2020-02-01