API Frame RegisterUnitEvent

Registers the frame for a specific event, triggering only for the specified units.
 registered = Frame:RegisterUnitEvent(eventName [, unit1, ...])
==Arguments==
:;eventName: - Name of the frame event.
:;unit1, ...: : UnitId - A list of units (up to four units).
==Returns==
:;registered:
==Details==
* Repeated calls will overwrite old registrations. Calling will also overwrite the old registration.
* If no unit is given, then all units will be watched; which is virtually the same as calling Frame:RegisterEvent.
==Example==
local function OnEvent(self, event, ...)
	print(event, ...)
end
local f = CreateFrame("Frame")
f:RegisterUnitEvent("UNIT_HEALTH", "player", "party1", "party2", "party3")
f:SetScript("OnEvent", OnEvent)
==Patch changes==