function looks for a widget whose name is the first component in the specified
names and that is a pop-up child of reference (or a normal child if reference
is a subclass of
It then uses that widget as the new reference and repeats the search
after deleting the first component from the specified names.
If it cannot find the specified widget,
Note that the names argument contains the name of a widget with respect to the
specified reference widget and can contain more than one widget name
(separated by periods) for widgets that are not direct children
of the specified reference widget.
If more than one child of the reference widget matches the name,
can return any of the children.
The Intrinsics do not require that all children of a widget have unique names.
If the specified names contain more than one component
and if more than one child matches the first component,
can return NULL if the single branch that it follows does not
contain the named widget.
does not back up and follow other matching branches of the widget tree.
function translates the specified window and display pointer into the
appropriate widget instance.