l-block">
(optional <strong>    (visitor,           *, boost::dfs_visitor&lt;&gt;())
    (root_vertex,       *, *vertices(graph).first)
    (index_map,         *, get(boost::vertex_index,graph))
    (in_out(color_map), *,
      default_color_map(num_vertices(graph), index_map) )</strong>
)
</pre>
</div>
<!-- @example.prepend('''
#include <boost/parameter.hpp>

namespace boost
{
  int vertex_index = 0;

  template <class T = int>
  struct dfs_visitor
  {};
}

BOOST_PARAMETER_NAME(graph)
BOOST_PARAMETER_NAME(