A class is created with the statement below. At which point does CPython invoke the metaclass's __prepare__, and what is its role in class body execution?
class Meta(type):
@classmethod
def __prepare__(mcs, name, bases, **kwds):
return {'injected': 99}
class A(metaclass=Meta):
pass
print(A.injected) # 99
print('injected' in A.__dict__) # True