The Application widget and widget tree

Each application has a top-level component called the Application widget, which is defined with the VtOpen(VTCL) command. This Application widget becomes the ``root'' of the ``widget tree'' -- a hierarchy of widgets for the given program.

Parents and children

Widgets within an application are presented as a hierarchy of components, with ``parent'' widgets managing layout and visibility of ``child'' widgets. For example, a menu button widget that is a child of a menu will not be visible if the parent menu is not visible.