diff --git a/docs/tech/tn0021.txt b/docs/tech/tn0021.txt
index 9a7d673e32..1bd5cafb5e 100644
--- a/docs/tech/tn0021.txt
+++ b/docs/tech/tn0021.txt
@@ -22,12 +22,12 @@ because then wxUSE_FOO would be not defined at all if the user directly
 includes wx/foo.h, include "wx/defs.h" before testing for wxUSE_FOO.
 
 
-2. Required files update
-------------------------
+2. Files to update
+------------------
 
-Assuming wxUSE_FOO is used on all platforms, the following must be done:
+The following files need to be modified when adding a new wxUSE_FOO:
 
-a) update include/wx/setup_inc.h
+a) include/wx/setup_inc.h
 
    This file contains all common wxUSE_XXXs, and is used to update wxMSW, wxMac
    setup.h and Unix setup.h.in using build/update-setup-h. Please try to add
@@ -39,13 +39,26 @@ a) update include/wx/setup_inc.h
    After changing this file, run the update-setup-h script (this is probably
    better done on a Unix machine although it should work under Cygwin too).
 
-b) update other setup.h files
+a') include/wx/msw/setup_inc.h for MSW-specific options
 
-   Currently include/wx/univ/setup.h and setup.h_vms are not automatically
-   updated so please update them manually (or modify the update-setup-h script
-   to take care of them...).
+   This file contains MSW-specific options, so if the new option is only used
+   under MSW, add it here instead of include/wx/setup_inc.h. The rest of the
+   instructions is the same as above.
 
-c) update configure.in
+b) include/wx/chkconf.h
+
+   Add the check for wxUSE_FOO definedness in the corresponding (base or GUI)
+   section. Please keep the alphabetic order.
+
+   If there are any dependencies, i.e. wxUSE_FOO requires wxUSE_BAR and
+   wxUSE_BAZ, check for thme here too.
+
+b') include/wx/msw/chkconf.h for MSW-specific options
+
+   These options won't be defined for the other ports, so shouldn't be added to
+   the common include/wx/chkconf.h but to this file instead.
+
+c) configure.in
 
    Here you need to add DEFAULT_wxUSE_FOO define. It should be added in the
    block beginning after WX_ARG_CACHE_INIT line and should default to "no" for
@@ -59,12 +72,9 @@ c) update configure.in
    If you have a sample/foo which should be only built when wxUSE_FOO==1,
    then only add it to the SAMPLES_SUBDIRS if wxUSE_FOO=yes in configure.
 
+d) docs/doxygen/mainpages/const_wxusedef.h
 
-3. Documentation
-----------------
-
-Currently wxUSE_XXXs are documented in docs/latex/wx/wxusedef.tex and a few 
-important global ones are in docs/latex/wx/cppconst.tex.
+   Add a brief description of the new constant.
 
 
 === EOF ===