document.onkeydown = NavigateThrough;function NavigateThrough (event)    {    if (!document.getElementById) return;    if (window.event) event = window.event;        if (event.ctrlKey)            {               var link = null;               var href = null;               switch (event.keyCode ? event.keyCode : event.which ? event.which : null)                   {                       case 0x25:                               link = document.getElementById ('PrevLink');                               break;                       case 0x27:                               link = document.getElementById ('NextLink');                   }        if (link) document.location = link.href;            }    }