// Use the copy of revision ID in case this undocumented, shady hook tries to mess with internals. $this->getHookRunner()->onSkinTemplateBuildNavUrlsNav_urlsAfterPermalink( $this, $modifiedNavUrls, $revid, $revid );
This hook only exists to aid using BaseTemplateToolbox, in a situation where the hook user needs to check the revision to decide whether to add items into NavUrls/BaseTemplateToolbox or not. (for instance CiteThisPage, previously used it to check if title exists, albeit there are better ways of doing so)
The hook it's supposed to provide rev id for will soon be deprecated (T253416), and so this helper hook should be deprecated too.
The replacement for BaseTemplateToolbox (SidebarBeforeOutput hook) is sufficient to provide what both hooks used to provide, already demonstrated in b9bdc3fc19f1 for CiteThisPage extension and in the yet-to-be merged r601942