p level for the most important or
common definitions.</li>
</ul>

<p>For example,
<a href="https://doc.rust-lang.org/std/io/struct.IoError.html"><code>IoError</code></a>
is defined in <code>io/mod.rs</code>, since it pertains to the entirety of <code>io</code>,
while
<a href="https://doc.rust-lang.org/std/io/net/tcp/struct.TcpStream.html"><code>TcpStream</code></a>
is defined in <code>io/net/tcp.rs</code> and reexported in the <code>io</code> module.</p>

<h3 id='use-internal-module-hierarchies-for-organiza