function checkBalancedTags() {
 var text = document.getElementById( 'wpTextbox1' ).value;

 //check balanced tags
 //idea from http://blog.stevenlevithan.com/archives/get-html-summary
 var pattern = /<\s*(\/)?\s*(\w+)[^\/>]*(\/)?\s*>/g;
 var match;
 var openTags = [];
 var unclosedTags = []; //error list
 var unopenTags = []; //error list
 while( (match = pattern.exec( text ) ) ) {
  var closeTag = match[1];
  var tagName = match[2];
  var selfcloseTag = match[3];
  tagName = lc(tagName); //normalize
  //search tag in array
  for( var i = 0; i < tags.length; i++ ) {
   if( tags[i] == tagName ) { //valid Tag
    if( selfcloseTag ) {
     continue; //nothing to do
    }
    if( closeTag ) {
     var index = 0; //search for open tag
     while( index < openTags.length && openTags[index] != tagName ) {
      index++;
     }
     if( index < openTags.length ) { //found a open tag
      while( index > 0 ) {
       unclosedTags.push(openTags[0]); //add first tag to error list
       openTags.shift()
       index--;
      }
      openTags.shift(); //remove current tag
     } else {
      unopenTags.push(tagName); //add current tag to error list
     }
    } else {
     openTags.unshift(tagName); //add current tag
    }
   }
   break;
  }
 }
 //add left open tags to error list
 unclosedTags = unclosedTags.concat(openTags);
 if( unclosedTags.length > 0 ) {
  /* warning - unclosed tags */
  alert( "unclosed tags: " + unclosedTags );
 }
 if( unopenTags.length > 0 ) {
  /* warning - unopen tags */
  alert( "Unopen Tags: " + unopenTags );
 }
}

var tags = [
 //HTML
 'abbr',
 'b',
 'br',
 'big',
 'blockquote',
 'caption',
 'center',
 'cite',
 'code',
 'del',
 'div',
 'dd',
 'dl',
 'dt',
 'em',
 'font',
 'h1',
 'h2',
 'h3',
 'h4',
 'h5',
 'h6',
 'hr',
 'i',
 'ins',
 'ol',
 'p',
 'pre',
 'rb',
 'rp',
 'rt',
 'ruby',
 's',
 'small',
 'span',
 'strike',
 'strong',
 'sub',
 'sup',
 'table',
 'td',
 'th',
 'tr',
 'tt',
 'u',
 'ul',
 'var',
 //MediaWiki/Extension
 'categorytree',
 'charinsert',
 'hiero',
 'imagemap',
 'inputbox',
 'poem',
 'ref',
 'references',
 'source',
 'syntaxhighlight',
 'timeline'
];