Bug 196347

Created attachment 366164 [details] Testcase If you create a custom element with a shadow DOM with slot elements Safari will not insert the slotted content if the content was added before the slot elements - except if it's the initial content. This works in Firefox and Chrome. 1. Create a custom element with a shadow DOM and add it to the document. 2. Append a child to the custom element with a slot property. 3. Append a slot element to the custom element shadow DOM with the same slot name. The slotted element is properly rendered at this point. 4. Append another child to the custom element with a different slot property. 5. Append another slot element to the shadow DOM with the same slot name. Now nothing is rendered. When looking at the DOM everything looks correct. The shadow DOM has two slot elements and the custom element has two children with matching slot attributes. However the children are not inserted into the slots and not rendered at all. 6. Append another slot element to the custom element shadow DOM with a new slot name. 7. Append another child to the custom element with the same slot name. Now all slotted elements are rendered, including the one that was missing before. I'm attaching a small html file that can be use to see the problem.