SpellList does practically the same thing with its spell detection algorithm.
It has 2 modes hard coded in, one scans to the last known SpellID, and the other is for me to find the max SpellID for a given client build. The addon is released using the first mode.
As far as scanning and filtering, it uses a throttling method I developed that makes sure it only uses so much CPU time between frames to ensure the user has a somewhat decent FPS rate while it's working.