and we'll hide the tag types away in a nested
namespace, ``graphs::tag``.  The library provides a convenient
macro for that purpose. -->
<p>We're going to define our interface in namespace <tt class="docutils literal">graphs</tt>.  The
library provides a convenient macro for defining keyword objects:</p>
<pre class="literal-block">
#include &lt;boost/parameter/name.hpp&gt;

namespace graphs
{
  BOOST_PARAMETER_NAME(graph)    // Note: no semicolon
  BOOST_PARAMETER_NAME(visitor)
  BOOST_PARAMETER_NAME(root_v