Available from version 0.1 (Gerrit change 202801)
Add additional items to the X-Analytics header
Define function:
public static function onXAnalyticsSetHeader( OutputPage $out, array &$headerItems ) { ... }
Attach hook:
$wgHooks['XAnalyticsSetHeader'][] = 'MyExtensionHooks::onXAnalyticsSetHeader';
Called from:File(s): XAnalytics / XAnalytics.php
Function(s): generateHeader

For more information about attaching hooks, see Manual:Hooks.
For examples of other extensions using this hook, see Category:XAnalyticsSetHeader extensions.