Tibetan Four Immeasurables: what is the meaning of "happiness that knows no suffering"?

In Tibetan Buddhism, there are the Four Immeasurables, as follows: > The Four Immeasurables as a Traditional Tibetan Buddhist Prayer > > May all beings have happiness and the cause of happiness. > >May they be free of suffering and the cause of suffering. > >**May they never be disassociated from the supreme happiness which is without suffering**. > > May they remain in the boundless equanimity, free from both attachment to close ones and rejection of others. > >https://www.padmasambhava.org/sermon/four-immesurables/ What is the meaning above of "*the supreme happiness which is without suffering*"? Does it refer to Nirvana? Or does it refer to any type of wholesome happiness? If possible, please offer Tibetan or Sanskrit linguistic support for the answer.