OK, but the standard raid frames have a setting "show only dispellable debuffs". How do they do it?
In my case this setting has been unselected; nevertheless the party frames have displayed the debuffs on their top right corner and they all have been dispellable by my priest and druid - coincidence ?
Edit:
In addition, gamepedia seems to differ from wowpedia considerably
https://wow.gamepedia.com/API_UnitAura
http://wowwiki.wikia.com/wiki/API_UnitAura