<p>
The primary expression
</p>

<pre>
a[low : high]
</pre>

<p>
constructs a substring or slice. The <a href="#Core_types">core type</a> of
<code>a</code> must be a string, array, pointer to array, slice, or a
<a href="#Core_types"><code>bytestring</code></a>.
The <i>indices</i> <code>low</code> and
<code>high</code> select which elements of operand <code>a</code> appear