I assume this is how to do a basic buttonTemplate for the tabs macro -- I looked at the tab content currentTiddler template shown on the tiddlywiki documentation and postulated that same approach would work for a basic buttonTemplate. (The example showed wrapping a transclusion in the macro in a tiddler widget.)
the buttonTemplate code:
@@.ragsfiledisplay
<$transclude tiddler=<<currentTab>> field="caption">
<$macrocall $name="currentTab" $type="text/plain" $output="text/plain"/>
</$transclude>
@@
I didn't need a full blown custom template...
I just duplicated the macro's transclusion that was nested in the macro's buttonTemplate' transclusion *(hard to tell if the nested translusion was a fall-back or not), so I can wrap it in a css class for small caps font-variant-- adding the class to the tabs macro class parameter is not desired because I don't want it also being applied to the tabs' contents.
It works as far as I can tell...
I asssume this kind of basic template would allow me to create templates to change the caption transclusion to any field desired-- without cloning and hacking the tabs macro.