// at each node of those types.
func (m *Visitor) Visit(s *Structural) {
	m.visitStructural(s)
}

func (m *Visitor) visitStructural(s *Structural) bool {
	ret := false
	if m.Structural != nil {
		ret = m.Structural(s)
	}

	if s.Items != nil {
		m.visitStructural(s.Items)
	}
	for k, v := range s.Properties {
		if changed := m.visitStructural(&v); changed {
			ret = true
			s.Properties[k] = v
		}
	}