<screen xmlns="http://www.scons.org/dbxsd/v1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">% <userinput>scons -Q define=FOO</userinput>
cc -o prog.o -c -DFOO prog.c
% <userinput>scons -Q define=FOO define=BAR</userinput>
cc -o prog.o -c -DFOO -DBAR prog.c
</screen>
