Extension variable name:
<b>userCustom</b>
<br>
<br>
<b>Example:</b>
<br />
userCustom.onPreviewFinished = function() {
<br />
&nbsp;&nbsp;extensionMgr.onMessage(&quot;Finished!&quot;);
<br />
};
<br />
<br />
<a target="_blank"
	href="https://github.com/benweet/stackedit/blob/master/doc/developer-guide.md#architecture">More
	info</a>