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+<!--
+
+  Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 The SCons Foundation
+
+  Permission is hereby granted, free of charge, to any person obtaining
+  a copy of this software and associated documentation files (the
+  "Software"), to deal in the Software without restriction, including
+  without limitation the rights to use, copy, modify, merge, publish,
+  distribute, sublicense, and/or sell copies of the Software, and to
+  permit persons to whom the Software is furnished to do so, subject to
+  the following conditions:
+
+  The above copyright notice and this permission notice shall be included
+  in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+  KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+  WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+-->
+
+<!--
+
+=head1 Variant builds
+
+=head2 Variations on a theme
+
+Other variations of this model are possible. For example, you might decide
+that you want to separate out your include files into platform dependent and
+platform independent files. In this case, you'd have to define an
+alternative to C<$INCLUDE> for platform-dependent files. Most F<Conscript>
+files, generating purely platform-independent include files, would not have
+to change.
+
+You might also want to be able to compile your whole system with debugging
+or profiling, for example, enabled. You could do this with appropriate
+command line options, such as C<DEBUG=on>. This would then be translated
+into the appropriate platform-specific requirements to enable debugging
+(this might include turning off optimization, for example). You could
+optionally vary the name space for these different types of systems, but, as
+we'll see in the next section, it's not B<essential> to do this, since Cons
+is pretty smart about rebuilding things when you change options.
+
+-->
+
+  <para>
+
+  The &variant_dir; keyword argument of
+  the &SConscript; function provides everything
+  we need to show how easy it is to create
+  variant builds using &SCons;.
+  Suppose, for example, that we want to
+  build a program for both Windows and Linux platforms,
+  but that we want to build it in a shared directory
+  with separate side-by-side build directories
+  for the Windows and Linux versions of the program.
+
+  </para>
+
+  <scons_example name="ex_variants">
+    <file name="SConstruct" printme="1">
+    platform = ARGUMENTS.get('OS', Platform())
+
+    include = "#export/$PLATFORM/include"
+    lib = "#export/$PLATFORM/lib"
+    bin = "#export/$PLATFORM/bin"
+
+    env = Environment(PLATFORM = platform,
+                      BINDIR = bin,
+                      INCDIR = include,
+                      LIBDIR = lib,
+                      CPPPATH = [include],
+                      LIBPATH = [lib],
+                      LIBS = 'world')
+
+    Export('env')
+
+    env.SConscript('src/SConscript', variant_dir='build/$PLATFORM')
+    </file>
+    <directory name="src"></directory>
+    <directory name="src/hello"></directory>
+    <directory name="src/world"></directory>
+    <file name="src/SConscript">
+    Import('env')
+    SConscript('hello/SConscript')
+    SConscript('world/SConscript')
+    </file>
+    <file name="src/hello/SConscript">
+    Import('env')
+    hello = env.Program('hello.c')
+    env.Install('$BINDIR', hello)
+    </file>
+    <file name="src/hello/hello.c">
+    #include "world.h"
+    int main(int argc, char *argv[]) { printf "hello.c\n"; world(); }
+    </file>
+    <file name="src/world/SConscript">
+    Import('env')
+    world = env.Library('world.c')
+    env.Install('$LIBDIR', world)
+    env.Install('$INCDIR', 'world.h')
+    </file>
+    <file name="src/world/world.h">
+    #define STRING "world.h"
+    extern int world();
+    </file>
+    <file name="src/world/world.c">
+    int world() { printf "world.c\n"; }
+    </file>
+  </scons_example>
+
+  <para>
+
+  This SConstruct file,
+  when run on a Linux system, yields:
+
+  </para>
+
+  <scons_output example="ex_variants" os="posix">
+    <scons_output_command>scons -Q OS=linux</scons_output_command>
+  </scons_output>
+
+  <para>
+
+  The same SConstruct file on Windows would build:
+
+  </para>
+
+  <scons_output example="ex_variants" os="win32">
+    <scons_output_command>scons -Q OS=windows</scons_output_command>
+  </scons_output>
+
+  <!--
+
+  <scons_example name="ex_var2">
+    <file name="SConstruct" printme="1">
+    env = Environment(OS = ARGUMENTS.get('OS'))
+    for os in ['newell', 'post']:
+        SConscript('src/SConscript', variant_dir='build/' + os)
+    </file>
+  </scons_example>
+
+  <scons_output example="ex_var2">
+    <scons_output_command>scons -Q</scons_output_command>
+  </scons_output>
+
+  -->