Slot contract assertions (#40): injects sample light-DOM content targeting
each declared @slot, then checks that every declared slot has a matching
<slot> in the (open) shadow root and that the sample content projects into
it. Also flags shadow <slot>s that aren't documented with @slot. Mutates
the element's light DOM; intended for a throwaway mounted instance.
Slot contract assertions (#40): injects sample light-DOM content targeting each declared
@slot, then checks that every declared slot has a matching<slot>in the (open) shadow root and that the sample content projects into it. Also flags shadow<slot>s that aren't documented with@slot. Mutates the element's light DOM; intended for a throwaway mounted instance.