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 (Unix version) - 01 Dec 2021 19:32:36