ts will be displayed (default is
<code>TRUE</code>);</li>
<li><code>warning</code>: this option controls whether warning messages are displayed
(default is <code>TRUE</code>);</li>
<li><code>error</code>: this option controls whether error messages are displayed (default is
<code>FALSE</code>).</li>
</ul>
<p>By playing with <code>eval</code> and <code>echo</code> we can control whether our code is run and
displayed or any combination of these. For example, <code>eval = FALSE, echo = TRUE</code>
means our co