Example 1: Open specific internal/external links in new windows

In LocalSettings.php:

$wgLinkTargetParentClasses = [ 'foo', 'bar' ];

Adds target="_blank" as an attribute to links that are children of an HTML element that belong to either class "foo" or "bar". To use in the wiki:

This is some text with an <span class="foo">[[Internal link]]</span> and also an <span class="bar">[https://www.mediawiki.org External link]</span>.

In that example, both links will open in new windows or tabs.

Example 2: Open specific images in new windows

Using the same LocalSettings as in Example 1, in the wiki use:

<div class="bar">[[File:SomeImage|link=mediawiki.org]]</div>

Example 3: Open most links in a new window, but not these

$wgExternalLinkTarget = '_blank';
$wgLinkTargetParentClasses = [ 'foo', 'bar' ];
$wgLinkTargetDefault = '_self';

In the wiki:

[[This link]] will open in a new window, but not <span class="foo">[[this one]]</span>.

Example 4: Use with extensions

Surround extension parser functions or tags with some code and open any links generated by those extensions in a new window. As an example, we will use the Flickr API extension, with the LocalSettings code from Example 1:

<div class="foo"><flickr>SOMEIMAGEID</flickr></div>

Actually, that extension helpfully already surrounds any code that it generates with a class so really it is sufficient to set LocalSettings as follows:

$wgLinkTargetParentClasses = [ 'flickrapi' ];

This will apply to all Flickr images generated by the extension. When users click on any image, the link will open in a new window or tab.

Advanced

$wgLinkTargetParentClasses = [
     '_top' => [ 'foo' ],
     [ 'bar' ],
     '_parent' => 'baz'
];

Descendants of 'foo' will have target '_top', descendants of 'bar' will have target '_blank' and descendants of 'baz' will have target '_parent'.