Using '--' in comments

["Cliff Martin" <cmartin@cox.rr.com>]

I would like to know how I can make this well formed:

<?xml version="1.0" encoding="UTF-8"?>
<test>
        <!-- this command has one option --workdir -->
        <cmd>test.exe --workdir c:/test</cmd>
</test>

For some reason I can not use '--' in a comment. Is this by design, and if
so how do I overcome it?

Cliff Martin