Is UK transit visa required for a permanent resident in Schengen? [duplicate]

I have a permanent residence card from a Schengen country. Do I need any visa to arrive at Heathrow and transit to a SAS flight? From the rules I read at, there is a line in exceptions saying:

"a common format residence permit issued by an European Economic Area
(EEA) country or Switzerland"

The wording confuses me a bit. So asking to double check. Thanks