ally, the slice <code>y</code> is <code>[2 3]</code>,
	and the slice <code>x</code> is <code>[0]</code> with three free element slots (in other words, its capacity is 4),
</li>
<li>
	The 1st <code>append</code> call changes the slice <code>x</code> to <code>[0 2 3]</code> with one free element slot.
	And as the slice <code>x</code> and the array <code>a</code> share elements (before line 10),
	the array <code>a</code> is changed to <code>[0 2 3 3]</code>.
	The slice <code>y</code> and the array <code>a</cod