function ersetzen (str, wort, insertbefore, insertafter) {
            var expr = new RegExp('(<[^>]*)|' + wort, 'ig');
                 while (erg = expr.exec(str)) {
                  // alert(RegExp.leftContext + '[' + RegExp.lastMatch + ']' + RegExp.rightContext + ' (' + expr.lastIndex + ')');
                  if (RegExp.lastMatch.charAt(0) != '<' && RegExp.leftContext.substr(RegExp.leftContext.length - insertbefore.length) != insertbefore) {
                  str = RegExp.leftContext + insertbefore + RegExp.lastMatch + insertafter + RegExp.rightContext;
                 // alert('string geändert:\n\n' + str);
                 }
             }
    return str;
    }

window.onload = function () {
 document.body.innerHTML = ersetzen(document.body.innerHTML, 'SGG ', '<span class="markenname">', '</span>');
}