GtkTreeView::cursor-changed and GtkTreeSelection::changed do not send signals for changes during rubber-banding selection so here we capture motion-no

operator[](string)

recursive function to find the minimum (pre-computed / cached) width of a TreeViewItem tree

Windows actions lack the ability to toggle visibility. To support this, menus must be destroyed and recreated when toggling any action's visibility.

it is necessary to compute the minimum width necessary to show all items in a tree, before a horizontal scroll bar must be shown. this is because GTK2

accept button clicked, or enter pressed inside file name field also called by table view activate after special case handling