hese Boost PP data types unless otherwise noted. See the
      help for Boost PP for any explanation of these data types.
    </p>
<p>
      The term 'sequence' refers to a sequence of VMD data types and is not the same
      as a Boost PP sequence which is always referred to in this documentation as
      a 'seq'.
    </p>
<p>
      The term 'return' refers to the expansion of a macro. I use the terminology
      of a macro "returning some data" rather than the terminology of a
      macro "expanding to so