In this example, we're using the linkToAbsolute method to convert the relative URL '/about' into an absolute URL based on the base URL 'https://example.com'. The package library for linkToAbsolute is OCP\Util. This is one of the utility functions provided by the OCP (ownCloud platform) library, which is a set of PHP classes and functions for building web applications. The OCP library is commonly used in ownCloud and Nextcloud, but can also be used independently in any PHP project.