<!DOCTYPE html>
<html lang="en-US">
<head><title>Must Have Required Owned Elements</title></head>
  <body>
    <!--
    URL: https://www.w3.org/TR/wai-aria-1.2/#mustContain
    RULE: "There may be times that required owned elements are missing,
    * for example, while editing or while loading a data set. When a widget is
    * missing required owned elements due to script execution or loading,
    * authors MUST mark a containing element with aria-busy equal to true. For
    * example, until a page is full