ml">catchError</a>) is handling any errors thrown by either <code>foo</code> or <code>bar</code>.
If the error-handler had been registered as the <code>onError</code> parameter of
the <code>then</code> call, it would not catch errors from the <code>bar</code> call.</p>
<p>Futures can have more than one callback-pair registered. Each successor is
treated independently and is handled as if it was the only successor.</p>
<p>A future may also fail to ever complete. In that case, no callbacks are
called.</p>
   