The generic function pane-initial-focus returns the child of pane-with-children that has the input focus when pane-with-children is first displayed.
(setf pane-initial-focus) may be used to set the initial focus pane, but only before pane-with-children has been created. If the setter is called after pane-with-children has been created, an error is signalled.
pane-with-children should be a pane with child panes such as a layout, an interface, a button-panel or a toolbar.