code: function createIframeDocument ( iframe, documentStyles ) {
      if ( varExists( $ ) && iframe instanceof $ ) iframe = iframe[0];
  
      if ( ! iframe.ownerDocument.body.contains( iframe ) ) throw new Error( "The iframe has not been appended to the DOM, or is not a descendant of the body element. Can't create an iframe content document." );
      if ( ! iframe.contentDocument ) throw new Error( "Cannot access the iframe content document. Check for cross-domain policy restrictions." );
  
      documentStyles = documentStyles ? '<style type="text/css">\n' + documentStyles + '\n</style>\n' : "";
      iframe.contentDocument.write( '<!DOCTYPE html>\n<html>\n<head>\n<meta charset="UTF-8">\n<title></title>\n' + documentStyles + '</head>\n<body>\n</body>\n</html>' );
  
      return iframe.contentDocument;
  }
docs: Creates an iframe document with an HTML5 doctype and UTF-8 encoding.
  
  The iframe element MUST have been appended to the DOM by the time this function is called, and it must be a
  descendant of the body element. A document inside an iframe can only be created when these conditions are met.
  
  @param   {HTMLIFrameElement|jQuery}  iframe
  @param   {string}                    [documentStyles]  cssText string of CSS rules, styles the iframe document, e.g.
  "html, body { overflow: hidden; } div.foo { margin: 2em; }"
  @returns {Document}