ched to any point in the grammar specification.
          These actions are C++ functions or function objects that are called whenever
          a part of the parser successfully recognizes a portion of the input. Say
          you have a parser <code class="computeroutput"><span class="identifier">P</span></code>, and
          a C++ function <code class="computeroutput"><span class="identifier">F</span></code>. You can
          make the parser call <code class="computeroutput"><span class="identifier">F<