!!! Overview[1]
[{$pagename}]  is an implementation of the [browser-view] pattern, providing a secure [browser-view] displayed in the context of the [application].

[{$pagename}] was added in [iOS] 9

[{$pagename}] class has all the properties of the [system browser], and is an '[external User-Agent]', even though it is presented within the host [application].  

Regardless of whether the user completes the request in the [system browser] (as is their choice), or the [{$pagename}], the return of the [token] via [Private-Use URI Scheme Redirection] or [Claimed Https Scheme URI Redirection] the link is the same.

Why [{$pagename}] vs [WebView]
[{$pagename}] was developed to stop developers from creating fragmentation by developing custom mini-browsers to run in-app browser content on [iOS], [Apple] has introduced the Safari View Controller in iOS9 (September [2015|Year 2015]), which is a “sandboxed” version of [Safari]. It gives the developer a standardized environment in which to present content, while offering the user a consistent experience and several convenient security helpers that allow users, for [example], to log in to a View Controller and stay logged in when visiting a related site in mobile Safari by means of shared [cookies] and shared login [credentials]. 

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [SFSafariViewController|https://developer.apple.com/library/prerelease/ios/documentation/SafariServices/Reference/SFSafariViewController_Ref/index.html/|target='_blank'] - based on information obtained 2016-03-18-