The following code is flagged as dead (since it's *replacing* rather than updating the existing Object):
https://github.com/mozilla/pdf.js/blob/4483cba72410027acf46630ebf252ae529704476/src/core/xfa/template.js#L2336-L2339
according to the alert in https://github.com/mozilla/pdf.js/security/code-scanning/103?query=ref%3Arefs%2Fheads%2Fmaster

Looking at the surrounding code, I can see a couple of possibilities here:
 1. This is indeed just dead code, which should be removed.
 2. The code should be moved up, and placed just *above* the previous block instead.
 3. There should be other, more invasive, changes made to this code...

/cc @calixteman Which solution is correct here?
Assuming it's either option 1 or 2, I can submit a patch to fix this.
if (!this.subform.children.length) {
      return HTMLResult.success({
        name: "div",
        children: [],
      });
    }
    this[$extra] = {
      overflowNode: null,
      firstUnsplittable: null,
      currentContentArea: null,
      currentPageArea: null,
      noLayoutFailure: false,
      pageNumber: 1,
      pagePosition: "first",
      oddOrEven: "odd",
      blankOrNotBlank: "nonBlank",
      paraStack: [],
    };
    const root = this.subform.children[0];
    root.pageSet[$cleanPage]();
    const pageAreas = root.pageSet.pageArea.children;
    const mainHtml = {
      name: "div",
      children: [],
    };
    let pageArea = null;
    let breakBefore = null;
    let breakBeforeTarget = null;
    if (root.breakBefore.children.length >= 1) {
      breakBefore = root.breakBefore.children[0];