ass</var> are both <a href="ref-glossary.html#gl:unit-class">unit&nbsp;classes</a> and no
space-instances value is supplied to <nobr><b>change-class</b></nobr>, the changed
<var>instance</var> remains on all <a href="ref-glossary.html#gl:space-instance">space&nbsp;instances</a> that allow
<var>new-class</var> <a href="ref-glossary.html#gl:instances">unit&nbsp;instances</a>.  In addition, <var>instance</var> is
also added to all space instances defined as initial-space-instances for
<var>new-class</var>.  If