i've been poking around zimlets for a little time now and am wondering whether it is possible to add, via a zimlet, a button to the menu toolbar that you see when you login to zimbra. 
Are there any sample zimlets that do this? From the ones I've tinkered with, I didn't see any that had a button added.
There is some sparse wiki documentation on this subject:
Creating a Menu Bar - Zimbra :: Wiki
and some discussion which seems very promising on this subject:
DwtButton - Zimbra :: Wiki
DwtMenu - Zimbra :: Wiki
DwtMenuItem - Zimbra :: Wiki
However, I'd like to see this in the context of a real example since I'm new to zimbra and js.
I've found some files in this zimbra directory, which seem to have the elements for a button [which I found are called 'Tabs']: zimbra/trunk/ZimbraWebClient/WebRoot/js/zimbraMail/calendar/view
Why I'm doing this / if you want to understand:
I'm trying to add accessibility options, so when the button is pushed, I want to 'save' and reflect the button is pushed. It seems that I can do this by replacing the image on a click.
more exactly, I detail what I'm talking about via the following images:
or specifically maybe something within a 'submenu' or 'category', like the calendar: