dialog_item ->
reference: [point]Reference point for alignment in two-dimensional grid. When to items are
aligned horizontally or vertically, dialog->layout
aligns the
graphical<-x or graphical<-y
component of their reference points.
The get-method returns the value of the variable when filled and
fails otherwise. This method is redefined by most dialog-item subclasses
(button<-reference, text_item<-reference,
etc.).
Invoking dialog_item->reference: @default
will make the item return its class-defined default. Invoking this
method with an instance of class point
will explicitly set the reference-point.
