Opening lazily creates an activated subwindow below the object, adds it
to the application and initializes the editor from the preview
specification. An existing window is reused without resampling the
preview. Internal Open returns one even on construction/open failure;
failed opening of a created window invokes cancellation.
OK copies the editor specification into the preview before removing and
disposing the window. Cancel and window close requests discard edits.
Notifications enqueue the private close method through
Application_PushMethod. Hide only delegates: its local window-closing
code is compiled out. DisconnectParent cancels an existing popup before
superclass disconnection.