Consider the following piece of JavaScript code:
<ol class="dp-xml" start="1">
 	<li class="alt"><span class="tag">&lt;</span><span class="tag-name">script</span><span class="tag">&gt;</span></li>
 	<li class="alt">function fun(0){</li>
 	<li class="">    if(<span class="attribute">0</span>===undefined)</li>
 	<li class="alt">        debugger;</li>
 	<li class="alt">}</li>
 	<li class="alt"><span class="tag">&lt;/</span><span class="tag-name">script</span><span class="tag">&gt;</span></li>
</ol>
What is the role of the "debugger" statement?