Element: ariaRequired プロパティ

<div id="txtboxMultilineLabel">Enter the tags for the article</div>
<div
  role="textbox"
  id="txtBoxInput"
  contenteditable="true"
  aria-multiline="true"
  aria-labelledby="txtboxMultilineLabel"
  aria-required="true"></div>

let el = document.getElementById("txtBoxInput");
console.log(el.ariaRequired); // "true"
el.ariaRequired = "false";
console.log(el.ariaRequired); // "false"