`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
beforeAll(async () => {
      pages = await loadAndWait("issue12706.pdf", "[data-annotation-id='63R']");
    });
    afterAll(async () => {
      await closePages(pages);
    });
    it("must let checkboxes with the same name behave like radio buttons", async () => {
      const selectors = [63, 70, 79].map(n => `[data-annotation-id='${n}R']`);
      await Promise.all(
        pages.map(async ([browserName, page]) => {
          for (const selector of selectors) {
            await page.click(selector);
            await page.waitForFunction(
              `document.querySelector("${selector} > :first-child").checked`
            );
            for (const otherSelector of selectors) {
              const checked = await page.$eval(
                `${otherSelector} > :first-child`,
                el => el.checked
              );
              expect(checked)
                .withContext(`In ${browserName}`)
                .toBe(selector === otherSelector);
            }
          }
        })
      );
    });
  });
});