export class rule
===

recently i have been wondering why can we use mfc's class while it seems not to export its class,cause i know we can export a class using  __declspec(dllimport),for example:
i define a class CBaseClass in a dll named test.dll,then i use it as a base class in my test.exe;before i can use CBaseClass i should first export it from test.dll;so i think that ruld should apply to mfc;but i don't see that anywhere in mfc's source code ,anyboy can shed a light on this ,thanks 
 

    class CWnd:public CCmdTarget
    {
    }

there is no __declspec(dllimport),they why can we use it in our project