Re: [svgwg] Remove instanceRoot and animatedInstanceRoot? (#852)

It's not implemented anywhere. 
We need to remove it from the spec and
from https://wpt.fyi/results/svg/idlharness.window.html


- Spec declares them: struct.html:3293-3294 (IDL) + prose at 3308-3317 ("u.instanceRoot is equivalent to getting u.shadowRoot.firstChild").
- WPT asserts them: interfaces/SVG.idl:301-302 + idlharness.window.js:114 tests SVGUseElement, so the missing members force-fail.
- No engine ships them 

Note an extra nail in the coffin for the removal argument: the `<use>` UA shadow root is closed, so `u.shadowRoot` returns null in practice. The spec's own "equivalent to u.shadowRoot.firstChild" definition can't even execute from author script.


<table id="out"><tbody><tr><td>use.shadowRoot</td><td class="val">null</td></tr><tr><td>'instanceRoot' in use</td><td class="val">false</td></tr><tr><td>'animatedInstanceRoot' in use</td><td class="val">false</td></tr><tr><td>typeof use.instanceRoot</td><td class="val">undefined</td></tr><tr><td>use.shadowRoot.firstChild (spec equivalent)</td><td class="val">TypeError: null is not an object (evaluating 'use.shadowRoot.firstChild')</td></tr></tbody></table>

with 

```html
<svg xmlns="http://www.w3.org/2000/svg" width="0" height="0" style="position:absolute">
  <rect id="r"/>
  <use href="#r"/>
</svg>

<script>
const use = document.querySelector("use");

const checks = [
  ["use.shadowRoot",
    () => String(use.shadowRoot)],                    // null — closed UA shadow root
  ["'instanceRoot' in use",
    () => String("instanceRoot" in use)],             // false — not implemented
  ["'animatedInstanceRoot' in use",
    () => String("animatedInstanceRoot" in use)],     // false — not implemented
  ["typeof use.instanceRoot",
    () => typeof use.instanceRoot],                    // "undefined"
  ["use.shadowRoot.firstChild (spec equivalent)",
    () => { try { return "→ " + String(use.shadowRoot.firstChild); }
            catch (e) { return e.name + ": " + e.message; } }],  // TypeError
];
</script>
```

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Received on Sunday, 28 June 2026 02:57:57 UTC