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