 value will be appended.
The previous behavior can be recreated by adding a <code>nil</code> argument to the call.
</p>

<p>
<em>Updating</em>:
Existing implementations of <code>hash.Hash</code> will need to add a
<code>BlockSize</code> method.  Hashes that process the input one byte at
a time can implement <code>BlockSize</code> to return 1.
Running <code>go</code> <code>fix</code> will update calls to the <code>Sum</code> methods of the various
implementations of <code>hash.Hash</code>.
</p>

<p>
<em>Upda