function wufoo_shortcode( $atts ) {
  $attr = shortcode_atts(
    array(
      'username'   => '',
      'formhash'   => '',
      'autoresize' => true,
      'height'     => '500',
      'header'     => 'show',
    ),
    $atts
  );

  // Check username and formhash to ensure they only have alphanumeric characters or underscores, and aren't empty.
  if (
    ! preg_match( '/^[a-zA-Z0-9_]+$/', $attr['username'] )
    || ! preg_match( '/^[a-zA-Z0-9_]+$/', $attr['formhash'] )
  ) {
    /*
		 * Return an error to the users with instructions if one of these params is invalid
		 * They don't have default values because they are user/form-specific
		 */
    if ( current_user_can( 'edit_posts' ) ) {
      return sprintf(
        wp_kses(
          /* translators: URL to Wufoo support page. */
          __( 'Something is wrong with your Wufoo shortcode. Try following the instructions <a href="%s" target="_blank" rel="noopener noreferrer">here</a> to embed a form on your site.', 'jetpack' ),
          array(
            'a' => array(
              'href'   => array(),
              'target' => array(),
              'rel'    => array(),
            ),
          )
        ),
        'https://help.wufoo.com/articles/en_US/kb/Embed'
      );
    }
  }

  
/**
 * Placeholder which will tell Wufoo where to render the form.
 */
  $js_embed_placeholder = sprintf(
    '<div id="wufoo-%s"></div>',
    esc_attr( $attr['formhash'] )
  );

  
/**
 * Required parameters are present.
 * An error will be returned inside the form if they are invalid.
 */
  $js_embed = sprintf(
    '(function(){try{var wufoo_%1$s = new WufooForm();wufoo_%1$s.initialize({"userName":"%2$s","formHash":"%1$s","autoResize":"%3$s","height":"%4$d","header":"%5$s","ssl":true,"async":true});wufoo_%1$s.display();}catch(e){}})();',
    esc_attr( $attr['formhash'] ),
    esc_attr( $attr['username'] ),
    esc_attr( $attr['autoresize'] ),
    absint( $attr['height'] ),
    esc_js( $attr['header'] )
  );

  // Embed URL.
  $embed_url = sprintf(
    'https://%1$s.wufoo.com/embed/%2$s/',
    $attr['username'],
    $attr['formhash']
  );

  // Form URL.
  $form_url = sprintf(
    'https://%1$s.wufoo.com/forms/%2$s/',
    $attr['username'],
    $attr['formhash']
  );

  /*
	 * iframe embed, loaded inside <noscript> tags.
	 */
  $iframe_embed = sprintf(
    '<iframe height="%1$d" src="%2$s" allowTransparency="true" frameborder="0" scrolling="no" style="width:100%;border:none;">
			<a href="%3$s" target="_blank" rel="noopener noreferrer">%4$s</a>
		</iframe>',
    absint( $attr['height'] ),
    esc_url( $embed_url ),
    esc_url( $form_url ),
    esc_html__( 'Fill out my Wufoo form!', 'jetpack' )
  );

  wp_enqueue_script(
    'wufoo-form',
    'https://www.wufoo.com/scripts/embed/form.js',
    array(),
    JETPACK__VERSION,
    true
  );
  wp_add_inline_script( 'wufoo-form', $js_embed );

  
/** This action is already documented in modules/widgets/gravatar-profile.php */