osx man page for tk_class

Tk_SetClass(3)						       Tk Library Procedures						    Tk_SetClass(3)

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NAME
       Tk_SetClass, Tk_Class - set or retrieve a window's class

SYNOPSIS
       #include <tk.h>

       Tk_SetClass(tkwin, class)

       Tk_Uid
       Tk_Class(tkwin)

ARGUMENTS
       Tk_Window tkwin (in)	      Token for window.

       char *class (in) 	      New class name for window.
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DESCRIPTION
       Tk_SetClass is called to associate a class with a particular window.  The class string identifies the type of the window;  all windows with
       the same general class of behavior (button, menu, etc.) should have the same class.  By convention all class names  start  with	a  capital
       letter,	and there exists a Tcl command with the same name as each class (except all in lower-case) which can be used to create and manipu-
       late windows of that class.  A window's class string is initialized to NULL when the window is created.

       For main windows, Tk automatically propagates the name and class to the WM_CLASS property used by window  managers.   This  happens  either
       when a main window is actually created (e.g. in Tk_MakeWindowExist), or when Tk_SetClass is called, whichever occurs later.  If a main win-
       dow has not been assigned a class then Tk will not set the WM_CLASS property for the window.

       Tk_Class is a macro that returns the current value of tkwin's class.  The value is returned as a Tk_Uid, which may  be  used  just  like  a
       string  pointer	but also has the properties of a unique identifier (see the manual entry for Tk_GetUid for details).  If tkwin has not yet
       been given a class, then Tk_Class will return NULL.

KEYWORDS
       class, unique identifier, window, window manager

Tk																    Tk_SetClass(3)