code: func Walk(e *Entity, call func(path []string, l Literal) error) error {
  	for prop, val := range e.Objects {
  		err := walkObj(val, []string{string(prop)}, call)
  		if err != nil {
  			return errors.Wrap(err, "walking object")
  		}
  	}
  	return nil
  }
docs: // Walk recursively visits every Object in the Entity and calls "call" with
  // every Literal and it's path.