pub trait GroupExt: WidgetExt {
// Provided methods
fn begin(&self) { ... }
fn end(&self) { ... }
fn clear(&self) { ... }
fn add<W: WidgetExt>(&self, widget: &W)
where Self: Sized { ... }
fn remove<W: WidgetExt>(&self, widget: &W)
where Self: Sized { ... }
fn set_align_content(&self, align: AlignContent) { ... }
fn set_justify_content(&self, align: AlignContent) { ... }
fn children(&self) -> Vec<Box<dyn WidgetExt>> { ... }
}