code: def add_pseudo_fields(self):
          
          fields = []
          if self.backlight_on != enums.BACKLIGHT_ON_NEVER:
              fields.append(
                  display_fields.BacklightPseudoField(ref='0', backlight_rule=self.backlight_on)
              )
  
          fields.append(
              display_fields.PriorityPseudoField(
                  ref='0',
                  priority_playing=self.priority_playing,
                  priority_not_playing=self.priority_not_playing,
              )
          )
  
          self.pattern.add_pseudo_fields(fields, self.screen)
docs: Add 'pseudo' fields (e.g non-displayed fields) to the display.