static isFocusableElement() {
    let result = false;

    if (document.activeElement) {
      const isContentEditable =
          document.activeElement.contentEditable !== 'inherit' &&
          document.activeElement.contentEditable !== undefined;
      const isInput = ['INPUT', 'SELECT', 'OPTION', 'TEXTAREA']
          .indexOf(document.activeElement.tagName) > -1;
      result = isInput || isContentEditable;
    }

    return result;
  }
Checks whether the document has focus on an input or contenteditable
element.
@return {boolean} Whether the focused element is an input or content
editable.