Yes I saw these, what I mean to ask is who consumes these? I want to see examples of applicability to understand why/how are they convenient.

Ah, gotcha. When you send anObject magritteDescription these become the children of the returned container

Ah, I see:

buildContainer: anObject
	| containerPragmas containerPragma containerSelector extensionSelectors container |
	
	containerPragmas := Pragma 
		allNamed: self class containerPragma 
		from: anObject class to: Object.
		...

Another detail, I see MADynamicDescriptionCache is that mandatory? I notice it would create an IdentityDictionary and this works instance based and I'm worried about not really scaling by design on high diversity loads.

I’m not sure. I guess it’s an optimization to avoid repeatedly recreating the same description, which can be expensive. Per-instance makes sense because there is no guarantee that descriptions are identical for different instances of the same class.

All that said, it’s Smalltalk so everything is malleable if it doesn’t fit your use case.

From a few talks I heard, QC sounds pretty interesting, possibly taking some Magritte ideas a bit further. They tried to merge some stuff back into canonical, but it seems incomplete as you point out. That said, it never seems to cause any problems (at least for me in heavy long term use, but YMMV)