an class="emphasis"><em>enablers</em></span>
          are in namespace boost::spirit. The reason is that these placeholders are
          shared by other <a href="http://boost-spirit.com" target="_top">Spirit</a> <span class="emphasis"><em>domains</em></span>.
          <span class="emphasis"><em>Spirit.Qi</em></span>, the parser is one domain. <span class="emphasis"><em>Spirit.Karma</em></span>,
          the generator is another domain. Other parser technologies may be developed
          and placed in y