When a navigation is initiated by an Element (i.e., a link click or a form submission), the sourceElement property on the NavigateEvent will be the initiating element.
This was requested by web developers. It provides an easy way to disambiguate which of several possible elements initiated a navigation.
Explainers: https://github.com/WICG/navigation-api/commit/85edaf1d4d42355b020807cd56f6a22784978c3d