Hi nameless, the history button in the default UI is in SidePane.htm and it looks like this (I've marked it with >>> ):

                    <div id="EditTabContent">
                        <table>
                            <tr>
                                <td><moi:commandbutton icon="icons/JoinIcon.png" command="join"><moi:text textid="Join" /></moi:commandbutton></td>
                                <td><moi:commandbutton icon="icons/SeparateIcon.png" command="separate"><moi:text textid="Separate" /></moi:commandbutton></td>
                                <td><moi:commandbutton icon="icons/TrimIcon.png" command="trim"><moi:text textid="Trim" /></moi:commandbutton></td>
                                <td><moi:commandbutton icon="icons/ExtendIcon.png" command="extend"><moi:text textid="Extend" /></moi:commandbutton></td>
                            </tr>

                            <tr>
                                <td><moi:commandbutton icon="icons/ShowPointsIcon.png" command="showpoints"><moi:text textid="Show pts" /></moi:commandbutton></td>
                                <td><moi:commandbutton icon="icons/AddPointIcon.png" command="addpoint"><moi:text textid="Add pt" /></moi:commandbutton></td>
                                <td><moi:commandbutton icon="icons/CopyClipboardIcon.png" command="copyclipboard" rcommand="copyclipboardwithorigin"><moi:text textid="Copy clipboard" /></moi:commandbutton></td>
                                <td><moi:commandbutton icon="icons/PasteIcon.png" command="paste" rcommand="pastepart"><moi:text textid="Paste" /></moi:commandbutton></td>
                            </tr>

                            <tr>
                                <td><moi:commandbutton icon="icons/HideIcon.png" onclick="var gd = moi.geometryDatabase; if ( event.ctrlKey ) { gd.showSubset(); } else if ( event.button == 2 ) { gd.isolate(); } else { gd.hide(); }"><moi:text textid="Hide" /></moi:commandbutton></td>
                                <td><moi:commandbutton icon="icons/LockIcon.png" onclick="var gd = moi.geometryDatabase; if ( event.ctrlKey ) { gd.unlockSubset(); } else if ( event.button == 2 ) { gd.isolateLock(); } else { gd.lock(); }"><moi:text textid="Lock" /></moi:commandbutton></td>
>>>>>>>>>>>                     <td><moi:commandbutton icon="icons/HistoryIcon.png" command="history"><moi:text textid="History" /></moi:commandbutton></td>
                                <td></td>
                            </tr>
                        </table>
                    </div>

- Michael