Upgrade the specified element to be of the Dart type this was created for.
After upgrading the element passed in is invalid and the returned value should be used instead.
Element upgrade(Element element);
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/2.0.0/dart-html/ElementUpgrader/upgrade.html