There are two ways to implement tooltips in an interface toolbar:
:tooltips
initarg.
tooltips
should be a list containing a string for each button in the component. For an example of this see
(example-edit-file "capi/applications/simple-symbol-browser")
(setf print-button
(make-instance 'toolbar-button
:image :std-print
:text "Print Something"
:help-key 'foo))
(defun do-help (interface pane type help-key)
(when (eq type :tooltip)
(when (eq help-key 'foo)
"Tooltip help")))
(display
(make-instance
'interface
:toolbar-items
(list print-button)
:help-callback 'do-help))
CAPI User Guide and Reference Manual (Windows version) - 25 Feb 2015