[Q] How a method in a category added ?

[S.J.Chun]

Hi,
As you know, I'm trying to make gnustep run on Windows without problem... Now 
I've found another problem.
Category system does not work on Windows, for example, in EDCommon, a new 
method for NSString class is 
defined and implemented using category but when I use that method in a tool(a 
test program) the runtime says
NSInvalidArgumentException, reason: NSConstantString(instance) does not 
recognize stringByRemovingSurroun...
like message.

So, how an objc runtime add method in category? Thanks in advance.