http://boost.sourceforge.net/libs/graph/doc/using_adjacency_list.html#sec:ad... says: "Creating your own property types and properties is easy; just define a tag class for your new property. The property tag class will need to define num with a unique integer ID, and kind which should be either edge_property_tag, vertex_property_tag, or graph_property_tag." But the sample tag class below don't define num. Has this become obsolete? The book (on page 52) only mentions an enum, where the value (without _t) is set to "a unique #", then BOOST_INSTALL_PROPERTY is called, the example on the above page doesn't state a value here as well.