Macro described 

macro_rules! described {
    () => { ... };
}

Say that a described widget is its own type, inside its Widget impl: described!();.

Without it the adapter reaches the widget as dyn Widget, cannot downcast it, and builds it again on every change it is told about, so what the person was doing with it — the focus in a field, a drag, the menu a press opened — goes with it. Every described component of the toolkit answers this; component::tests builds each one from the catalogue and holds it to it.