ode>data</code> and <code>metadata</code> items hold the names of
entries in the object's data and metadata
slots, respectively, while <code>dataDerived</code> and
<code>metadataDerived</code> hold the names of related
things that can be derived from the object's contents.</p></li>
<li><p>If <code>i</code> is <code>"u1"</code> then the return value is <code>v[,1]</code>,
and similarly for <code>"u2"</code> and <code>"u3"</code>.</p></li>
<li><p>If <code>i</code> is <code>"a1"</code> then signal amplitude is