Nothing special at all. Unnamed sidebar blocks will show the text <Unnamed> instead of just showing nothing, thus making them renamable
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>{$lang_insert_image_title}</title>
<script language="javascript" type="text/javascript" src="../../tiny_mce_popup.js"></script>
<script language="javascript" type="text/javascript" src="../../utils/mctabs.js"></script>
<script language="javascript" type="text/javascript" src="../../utils/form_utils.js"></script>
<script language="javascript" type="text/javascript" src="../../utils/validate.js"></script>
<script language="javascript" type="text/javascript" src="jscripts/functions.js"></script>
<link href="css/advimage.css" rel="stylesheet" type="text/css" />
<base target="_self" />
</head>
<body id="advimage" onload="tinyMCEPopup.executeOnLoad('init();');" style="display: none">
<form onsubmit="insertAction();return false;" action="#">
<div class="tabs">
<ul>
<li id="general_tab" class="current"><span><a href="javascript:mcTabs.displayTab('general_tab','general_panel');" onmousedown="return false;">{$lang_advimage_tab_general}</a></span></li>
<li id="appearance_tab"><span><a href="javascript:mcTabs.displayTab('appearance_tab','appearance_panel');" onmousedown="return false;">{$lang_advimage_tab_appearance}</a></span></li>
<li id="advanced_tab"><span><a href="javascript:mcTabs.displayTab('advanced_tab','advanced_panel');" onmousedown="return false;">{$lang_advimage_tab_advanced}</a></span></li>
</ul>
</div>
<div class="panel_wrapper">
<div id="general_panel" class="panel current">
<fieldset>
<legend>{$lang_advimage_general}</legend>
<table class="properties">
<tr>
<td class="column1"><label id="srclabel" for="src">{$lang_insert_image_src}</label></td>
<td colspan="2"><table border="0" cellspacing="0" cellpadding="0">
<tr>
<td><input name="src" type="text" id="src" value="" onchange="showPreviewImage(this.value);" /></td>
<td id="srcbrowsercontainer"> </td>
</tr>
</table></td>
</tr>
<tr id="imagelistsrcrow">
<td class="column1"><label for="imagelistsrc">{$lang_image_list}</label></td>
<td colspan="2" id="imagelistsrccontainer"> </td>
</tr>
<tr>
<td class="column1"><label id="altlabel" for="alt">{$lang_insert_image_alt}</label></td>
<td colspan="2"><input id="alt" name="alt" type="text" value="" /></td>
</tr>
<tr>
<td class="column1"><label id="titlelabel" for="title">{$lang_advimage_title}</label></td>
<td colspan="2"><input id="title" name="title" type="text" value="" /></td>
</tr>
</table>
</fieldset>
<fieldset>
<legend>{$lang_advimage_preview}</legend>
<div id="prev"></div>
</fieldset>
</div>
<div id="appearance_panel" class="panel">
<fieldset>
<legend>{$lang_advimage_tab_appearance}</legend>
<table border="0" cellpadding="4" cellspacing="0">
<tr>
<td class="column1"><label id="alignlabel" for="align">{$lang_insert_image_align}</label></td>
<td><select id="align" name="align" onchange="changeAppearance();">
<option value="">{$lang_insert_image_align_default}</option>
<option value="baseline">{$lang_insert_image_align_baseline}</option>
<option value="top">{$lang_insert_image_align_top}</option>
<option value="middle">{$lang_insert_image_align_middle}</option>
<option value="bottom">{$lang_insert_image_align_bottom}</option>
<option value="texttop">{$lang_insert_image_align_texttop}</option>
<option value="absmiddle">{$lang_insert_image_align_absmiddle}</option>
<option value="absbottom">{$lang_insert_image_align_absbottom}</option>
<option value="left">{$lang_insert_image_align_left}</option>
<option value="right">{$lang_insert_image_align_right}</option>
</select>
</td>
<td rowspan="6" valign="top">
<div class="alignPreview">
<img id="alignSampleImg" src="images/sample.gif" alt="{$lang_advimage_example_img}" />
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</div>
</td>
</tr>
<tr>
<td class="column1"><label id="widthlabel" for="width">{$lang_insert_image_dimensions}</label></td>
<td nowrap="nowrap">
<input name="width" type="text" id="width" value="" size="5" maxlength="5" class="size" onchange="changeHeight();" /> x
<input name="height" type="text" id="height" value="" size="5" maxlength="5" class="size" onchange="changeWidth();" /> px
</td>
</tr>
<tr>
<td> </td>
<td><table border="0" cellpadding="0" cellspacing="0">
<tr>
<td><input id="constrain" type="checkbox" name="constrain" class="checkbox" /></td>
<td><label id="constrainlabel" for="constrain">{$lang_advimage_constrain_proportions}</label></td>
</tr>
</table></td>
</tr>
<tr>
<td class="column1"><label id="vspacelabel" for="vspace">{$lang_insert_image_vspace}</label></td>
<td><input name="vspace" type="text" id="vspace" value="" size="3" maxlength="3" class="number" onchange="changeAppearance();updateStyle();" />
</td>
</tr>
<tr>
<td class="column1"><label id="hspacelabel" for="hspace">{$lang_insert_image_hspace}</label></td>
<td><input name="hspace" type="text" id="hspace" value="" size="3" maxlength="3" class="number" onchange="changeAppearance();updateStyle();" /></td>
</tr>
<tr>
<td class="column1"><label id="borderlabel" for="border">{$lang_insert_image_border}</label></td>
<td><input id="border" name="border" type="text" value="" size="3" maxlength="3" class="number" onchange="changeAppearance();updateStyle();" /></td>
</tr>
<tr>
<td><label id="classlabel" for="classlist">{$lang_class_name}</label></td>
<td colspan="2">
<select id="classlist" name="classlist">
<option value="" selected>{$lang_not_set}</option>
</select>
</td>
</tr>
<tr>
<td class="column1"><label id="stylelabel" for="style">{$lang_advimage_style}</label></td>
<td colspan="2"><input id="style" name="style" type="text" value="" onchange="styleUpdated();" /></td>
</tr>
<!-- <tr>
<td class="column1"><label id="classeslabel" for="classes">{$lang_advimage_classes}</label></td>
<td colspan="2"><input id="classes" name="classes" type="text" value="" onchange="selectByValue(this.form,'classlist',this.value,true);" /></td>
</tr> -->
</table>
</fieldset>
</div>
<div id="advanced_panel" class="panel">
<fieldset>
<legend>{$lang_advimage_swap_image}</legend>
<input type="checkbox" id="onmousemovecheck" name="onmousemovecheck" class="checkbox" onclick="changeMouseMove();" />
<label id="onmousemovechecklabel" for="onmousemovecheck">{$lang_advimage_alt_image}</label>
<table border="0" cellpadding="4" cellspacing="0" width="100%">
<tr>
<td class="column1"><label id="onmouseoversrclabel" for="onmouseoversrc">{$lang_advimage_mouseover}</label></td>
<td><table border="0" cellspacing="0" cellpadding="0">
<tr>
<td><input id="onmouseoversrc" name="onmouseoversrc" type="text" value="" /></td>
<td id="onmouseoversrccontainer"> </td>
</tr>
</table></td>
</tr>
<tr id="imagelistoverrow">
<td class="column1"><label for="imagelistover">{$lang_image_list}</label></td>
<td id="imagelistovercontainer"> </td>
</tr>
<tr>
<td class="column1"><label id="onmouseoutsrclabel" for="onmouseoutsrc">{$lang_advimage_mouseout}</label></td>
<td class="column2"><table border="0" cellspacing="0" cellpadding="0">
<tr>
<td><input id="onmouseoutsrc" name="onmouseoutsrc" type="text" value="" /></td>
<td id="onmouseoutsrccontainer"> </td>
</tr>
</table></td>
</tr>
<tr id="imagelistoutrow">
<td class="column1"><label for="imagelistout">{$lang_image_list}</label></td>
<td id="imagelistoutcontainer"> </td>
</tr>
</table>
</fieldset>
<fieldset>
<legend>{$lang_advimage_misc}</legend>
<table border="0" cellpadding="4" cellspacing="0">
<tr>
<td class="column1"><label id="idlabel" for="id">{$lang_advimage_id}</label></td>
<td><input id="id" name="id" type="text" value="" /></td>
</tr>
<tr>
<td class="column1"><label id="dirlabel" for="dir">{$lang_advimage_langdir}</label></td>
<td>
<select id="dir" name="dir" onchange="changeAppearance();">
<option value="">{$lang_not_set}</option>
<option value="ltr">{$lang_advimage_ltr}</option>
<option value="rtl">{$lang_advimage_rtl}</option>
</select>
</td>
</tr>
<tr>
<td class="column1"><label id="langlabel" for="lang">{$lang_advimage_langcode}</label></td>
<td>
<input id="lang" name="lang" type="text" value="" />
</td>
</tr>
<tr>
<td class="column1"><label id="usemaplabel" for="usemap">{$lang_advimage_image_map}</label></td>
<td>
<input id="usemap" name="usemap" type="text" value="" />
</td>
</tr>
<tr>
<td class="column1"><label id="longdesclabel" for="longdesc">{$lang_advimage_long_desc}</label></td>
<td><table border="0" cellspacing="0" cellpadding="0">
<tr>
<td><input id="longdesc" name="longdesc" type="text" value="" /></td>
<td id="longdesccontainer"> </td>
</tr>
</table></td>
</tr>
</table>
</fieldset>
</div>
</div>
<div class="mceActionPanel">
<div style="float: left">
<input type="button" id="insert" name="insert" value="{$lang_insert}" onclick="insertAction();" />
</div>
<div style="float: right">
<input type="button" id="cancel" name="cancel" value="{$lang_cancel}" onclick="cancelAction();" />
</div>
</div>
</form>
</body>
</html>