How are performance classes for helicopters/rotorcraft defined? In helicopter/rotocraft literature, such as ICAO Annex 14 Volume II (how to design heliports), there's constant references to performance classes. How can I tell what performance class a helicopter is in?

So far the only definition I have found is: in the event of engine failure, Performance Class 1 helicopters should be able to land within the rejected take-off distance available or continue safe flight, while Performance Class 3 will require forced landing. (https://www.casa.gov.au/standard-page/project-os-1124-incorporation-performance-class-concepts-australian-helicopter). 

This is hard to apply to helicopters where I only have some basic specifications. Are there any other, easier to use, definitions for performance classes? I'm hoping for something like runway codes for aerodromes, which are derived from landing distances and wing spans of aircraft that use the runway.
Multi-engine helicopters have 3 Performance Classes defined at certification that is related to single engine performance and how this affects follow-on risks following an engine failure.  

Class 1 helicopters have massive reserve power and can continue flight on one engine.  They have engines that are way larger than necessary for normal operation and normally operate at a fraction of their power potential until called upon to do it all.  Risks following engine failure are low.

Class 2 helicopters have somewhat less reserve power, and can continue flight temporarily on one engine, but not indefinitely.  Risk factors are higher.

Class 3 helicopters have little reserve power and are generally forced down when one engine fails, although at a much gentler descent rate than an autorotation. Risk factors are highest. 

I was looking for a link that provides a good detailed description but haven't had much luck.