How is the Happiness track attribute determined?

[DJLProjects]

This isn't a data point that Spotify API provides and I don't see happiness listed on the index of this tool.

How is the happiness of a track determined?

[jtagcat]

Do a quick Ctrl-F

                  track.feats.sadness=  (1 - audio_feature.energy) * (1 - audio_feature.valence);
                  track.feats.happiness = audio_feature.energy * audio_feature.valence;
                  track.feats.anger = audio_feature.energy * (1 - audio_feature.valence);