docs: function load(url, successCallback, errorCallback) {
    const xhr = new XMLHttpRequest();
  
    // async, however scripts will be executed in the order they are in the
    // DOM to mirror normal script loading.
    xhr.open("GET", url, true);
    if ("overrideMimeType" in xhr) {
      xhr.overrideMimeType("text/plain");
    }
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4) {
        if (xhr.status === 0 || xhr.status === 200) {
          successCallback(xhr.responseText);
        } else {
          errorCallback();
          throw new Error("Could not load " + url);
        }
      }
    };
    return xhr.send(null);
  }