The <i>capacity</i> is a measure of that extent: it is the sum of
the length of the slice and the length of the array beyond the slice;
a slice of length up to that capacity can be created by
<a href="#Slice_expressions"><i>slicing</i></a> a new one from the original slice.
The capacity of a slice <code>a</code> can be discovered using the
built-in function <a href="#Length_and_capacity"><code>cap(a)</code></a>.