• Added support for shadow DOM! This includes shadow roots, slots, composed events, and more. (pmdartus)
• Added the element.toggleAttribute() method.
• Fixed XMLHttpRequest sometimes sending an empty request body after a preflight request. (andreasf)
• Fixed the formElement.form property to use an algorithm that also checks the form="" attribute, instead of always looking for the closest ancestor <form> element. (jamietre)
• Stopped swallowing errors when the canvas or canvas-prebuilt packages were installed, but failed to load. (joscha)