This function recursively descends the widget hierarchy
identified by the root node win and finds the first
widget that matches the specified target type.
findWidgetByType(win, gtkType = "GtkMenuBar", verbose = FALSE)TRUE.
Each call is given the widget as its only argument
and expected to return a logical value indicating whether the
widget matches or not. One can use a closure and always
return FALSE if one wants to iterate over all the
widgets and collect the matching ones.
NULL.
Information on Gtk is available from http://www.gtk.org.
gtkContainerGetChildren