It was possible to set a tooltip for a certain toolbar entry.
However, this hasn't been used since that tooltip needed to be repeated for each occurence of the same command.
Instead, a TooltipLabel property has been introduced lately (see 9c2f197e).

This doesn't affect extensions (They have their own format to specify toolbars).

Change-Id: I0f0fd05b310bb49dd5b4123e31d3e7fec997dd15