>> Gedit has text under tool-bar icons.  Some icons are not self-evident,
>> so text helps to understand what they do.  An option for icon/text/icon+text
>> would be nice for the Emacs tool-bar.
>
> Indeed.  But for uses like tabs, the icons might not be an option.

For the per-frame tab-bar, yes.

But for interior per-window tab-bars I am completely lost now
since there is too wide range of opinions how general they should be
and what they should do.

If a tab is just a little rectangle on the screen associated
with an action, then the tab-bar is indistinguishable from the
tool-bar, so we might need only tool-bars inserted into the window-tree.

This screenshot illustrates how interior per-window tool-bars and
tab-bars could look where the Info tab-bar displays Info-breadcrumbs
and the lower tab-bar switches into compilation like in Eclipse: