declaration a @protocol in objective-c

What means a word "USING" in declaration of @protocol开发者_C百科?

The declaration is:

@protocol  name

USING

// declaration of methods

@end

There's no using keyword in Objective-C.

Two possibilities:

• It's somewhere defined as a macro, in that case you have to look it up in your code. (Xcode helps you with this if you click on it using a right-click.)

• The file is actually Objective-C++. The using keyword comes from C++, but I don't think there's a special functionality in the context of @protocol.

Given the fact that it's written in capitals, I'd say it's a macro.