code: function ensureMetaViewport ( _window ) {
      var _document = ( _window || window ).document,
          head = _document.head || _document.getElementsByTagName( "head" )[0],
          query = _document.querySelectorAll( 'meta[name="viewport"]' ),
          el = query.length ? query[0] : undefined;
  
      if ( !el ) {
          el = _document.createElement( "meta" );
          el.name = "viewport";
          el.content = "width=device-width, initial-scale=1.0";
          head.appendChild( el );
      }
  
      return el;
  }
docs: Makes sure the meta viewport tag exists. Does not modify existing settings. Creates the tag if missing, with the
  default setting ("width=device-width, initial-scale=1.0").
  
  Returns the element.
  
  @param   {Window} [_window=window]
  @returns {HTMLElement}