Interface to be implemented by decorating proxies, in particular Spring AOP
proxies but potentially also custom proxies with decorator semantics.
Note that this interface should just be implemented if the decorated class
is not within the hierarchy of the proxy class to begin with. In particular,
a "target-class" proxy such as a Spring AOP CGLIB proxy should not implement
it since any lookup on the target class can simply be performed on the proxy
class there anyway.
Defined in the core module in order to allow
(and potential other candidates without spring-aop dependencies) to use it
for introspection purposes, in particular annotation lookups.