`annotation_layer.js` has logic to keep input elements in sync. The logic uses `document.getElementsByName` with [a name derived from the PDF](https://github.com/mozilla/pdf.js/blob/10a1db698047e612e8ae3da66d12a6c1ac5597a3/src/core/annotation.js#L407) to retrieve the set of related elements. This query is not namespaced, so if the viewer ever adds a `name` attribute to a checkbox or radio input in the page, then the PDF file can get it changed (without user interaction via the scripting interface). Fortunately, there doesn't appear to be any input/radio element in the default viewer code. A custom viewer can be affected by this bug, however.

I suggest to replace the `document.getElementsByTagName` calls with a function that checks that the elements are created by the `annotation_layer.js` code before returning them. There are several ways to do so, e.g. by adding a custom attribute to each input element.

## Seemingly generic property assignment
This code on its own looks dangerous because it allows the caller to overwrite any property
https://github.com/mozilla/pdf.js/blob/99e442941c16561e8826a925b164d79f4ad51fbf/src/display/annotation_layer.js#L684-L688
Fortunately, it is only called with a fixed key, so only the `value` property can be updated in response to user input events:
https://github.com/mozilla/pdf.js/blob/99e442941c16561e8826a925b164d79f4ad51fbf/src/display/annotation_layer.js#L732-L740

## Unchecking other checkboxes on checkbox state change
https://github.com/mozilla/pdf.js/blob/99e442941c16561e8826a925b164d79f4ad51fbf/src/display/annotation_layer.js#L979-L990

## Updating the abstract state (storage)
https://github.com/mozilla/pdf.js/blob/99e442941c16561e8826a925b164d79f4ad51fbf/src/display/annotation_layer.js#L1061-L1065

## Allowing scripts to uncheck checkbox/radio inputs
The others require user interaction to have any effect; this one allows scripts embedded in the PDF to run logic without user interaction.
https://github.com/mozilla/pdf.js/blob/99e442941c16561e8826a925b164d79f4ad51fbf/src/display/annotation_layer.js#L1073-L1077
describe("Text widget", () => {
  describe("issue13271.pdf", () => {
    let pages;
    beforeAll(async () => {
      pages = await loadAndWait("issue13271.pdf", "[data-annotation-id='24R']");
    });
    afterAll(async () => {
      await closePages(pages);
    });
    it("must update all the fields with the same value", async () => {
      const base = "hello world";
      await Promise.all(
        pages.map(async ([browserName, page]) => {
          await page.type("#\\32 5R", base);
          await page.waitForFunction(
            `document.querySelector("#\\\\32 4R").value !== ""`
          );
          await page.waitForFunction(
            `document.querySelector("#\\\\32 6R").value !== ""`
          );
          let text = await page.$eval("#\\32 4R", el => el.value);
          expect(text).withContext(`In ${browserName}`).toEqual(base);
          text = await page.$eval("#\\32 6R", el => el.value);
          expect(text).withContext(`In ${browserName}`).toEqual(base);
        })
      );
    });
  });
});