Interesting cases - [foster parenting](https://html.spec.whatwg.org/#foster-parent) - [adoption agency algorithm](https://html.spec.whatwg.org/#adoption-agency-algorithm) - [reconstruct the active formatting elements](https://html.spec.whatwg.org/#reconstruct-the-active-formatting-elements) - [metadata elements after `</head>`](https://html.spec.whatwg.org/#the-after-head-insertion-mode) - [breaking out of foreign content](https://html.spec.whatwg.org/#parsing-main-inforeign)
