<pre>
func (p T) Lock() { … }
func (p T) Unlock() { … }
</pre>

<p>
they implement the <code>Locker</code> interface as well
as the <code>File</code> interface.
</p>

<h4 id="Embedded_interfaces">Embedded interfaces</h4>

<p>
In a slightly more general form
an interface <code>T</code> may use a (possibly qualified) interface type
name <code>E</code> as an interface element. This is called