content inside the contentPane is controlled by the client screen manager. It is dynamic and content gets switched in and out of it based on interaction with the server or with the user. It isn't actually set up for external event handlers. One of the reasons being the tracking of connected event handlers and their corresponding disconnection when content is destroyed (to allow the GC to clean up and prevent memory leaks).
The attribute 'mxid' you find inside forms is a custom identifier that is unique per form, whereas the 'id' attribute has to be unique per document. Using id would make it, ah, technically challenging to have multiple instances of the same form in the browser.
Where exactly are you trying to apply this rollover behaviour (which widgets/nodes)?
btw, many thanks for the LogoViewer (worked really well!).
re: We have some action trigger buttons where we've added a secondary style class "myClass". This allows me to style the action button with a given image by selecting those specific table cells instead of going directly to a "ViewButton" class div. So basically I have something like this:
<td class="TableColumn myClass"> <div class="ViewButton" mxid="actionTrigger1"> <span id="mendix_widget_MxButton_0" validate="none" progressbar="none" mxaction="onclick:do_some_action" dojotype="mendix.widget.MxButton" async="false" mxcontext="4" content_id="825" widgetid="mendix_widget_MxButton_0"> </span> </div> </td>
.myClass .ViewButton span