Stefan Kangas <stefan@marxist.se> writes:

> According to commit d2bd51898e4 the :vert-only property for toolbar
> items is supposed to be "for tool bar items with labels not shown
> horizontally".
>
> These properties are used in some places in our sources, but are not
> documented in (info "(elisp) Tool Bar").
>
> They also don't seem to be working, at least not in GTK:

Here's how the default toolbar looks for me: