so this is the secret sauce!
Using this attribute solves another overload resolution of generic vs. "existential" problem.
So this attribute is for when the compiler cannot decide which overload it should "favor". I wonder why the compile not just favor generic over "existential" in the case I just linked to?
Another question is with this attribute, it can break tie of two, what happen if there are more than two overloads? Say three? Seems it needs to take a "prirority" value to work this out?