lib/jsdom/living/helpers/shadow-dom.js
function retarget(a, b) {
  while (true) {
    if (!isNode(a)) {
      return a;
    }

    const aRoot = getRoot(a);
    if (
      !isShadowRoot(aRoot) ||
      (isNode(b) && isShadowInclusiveAncestor(aRoot, b))
    ) {
      return a;
    }

    a = getRoot(a).host;
  }
}
function retarget(a, b) {
  while (true) {
    if (!isNode(a)) {
      return a;
    }

    const aRoot = getRoot(a);
    if (
      !isShadowRoot(aRoot) ||
      (isNode(b) && isShadowInclusiveAncestor(aRoot, b))
    ) {
      return a;
    }

    a = getRoot(a).host;
  }
}
https://dom.spec.whatwg.org/#retarget