th <code>[[</code> method, the procedure works in steps.</p>
<p>First, the <code>metadata</code> slot of <code>x</code> is checked to
see whether it contains something named with <code>i</code>.
If so, then the named item is replaced with <code>value</code>.</p>
<p>Otherwise, if the string value of <code>i</code> ends in <code>Unit</code>, then the
characters preceding that are taken as the name of a variable, and
the <code>metadata</code> slot of <code>x</code> is updated to store that unit, e.g.</p>
<p></