nd never takes an argument.
</p>

<p>
What REF really is is a convenience.  One could, for example, put a
reference in a footnote by doing
<br/>
<span class="pre-in-pp">
  .FOOTNOTE
  .[
  keyword(s)
  .]
  .FOOTNOTE OFF
</span>
However, if you have a lot of references going into footnotes (or
endnotes), it&#8217;s much shorter to type <kbd>.REF/.REF</kbd>
than <kbd>.FOOTNOTE/.FOOTNOTE&nbsp;OFF</kbd>.  It also helps you
distinguish&mdash;visually, in your input file&mdash;between
footnotes (or endnotes) whi