f a default parser or a default generator from a given attribute type.
          It implements a minimal set of predefined mappings from different attribute
          types to parsers and generators (for a description of the predefined mappings
          see <a class="link" href="../../qi/reference/auto.html#spirit.qi.reference.auto.additional_requirements">Additional
          Attribute Requirements for Parsers</a> and <a class="link" href="../../karma/reference/auto.html#spirit.karma.reference.auto.additi