It's optimized for performance, so nothing fancy.
By default it's enabled only in dungeons and raids. The reason for that is that it's not iterating over debuffs to get the real duration, all durations are hardcoded. This makes it not suitable for PvP. And in the open world going far enough from a CC'd mob for it to disappear on your client and then coming back fires a SPELL_AURA_APPLIED CLEU event, causing the aura's bar to restart.