clang API Documentation
ObjCProtocolDecl - Represents a protocol declaration. ObjC protocols declare a pure abstract type (i.e no instance variables are permitted). Protocols originally drew inspiration from C++ pure virtual functions (a C++ feature with nice semantics and lousy syntax:-). Here is an example:
This says that NSDraggingInfo requires two methods and requires everything that the two "referenced protocols" 'refproto1' and 'refproto2' require as well.