function checkform(of)
        {
        // Test if DOM is available and there is an element called required
            if(!document.getElementById || !document.createTextNode){return;}
            if(!document.getElementById('required')){return;}

        // Define error messages and split the required fields
            var errorID='errormsg';
            var errorClass='error'
/* changes for linked list */
            var errorMsg='Vyplňte prosím správně tato pole:';
/* end changes for linked list */
            /*var errorImg='_images/alert.gif';*/
            var errorAlt='! ';
            var errorTitle='Toto pole není vyplněno správně!';
            var reqfields=document.getElementById('required').value.split(',');

        // Cleanup old mess
            // if there is an old errormessage field, delete it
            if(document.getElementById(errorID))
            {
                var em=document.getElementById(errorID);
                em.parentNode.removeChild(em);
            }
            // remove old images and classes from the required fields
            for(var i=0;i<reqfields.length;i++)
            {
                var f=document.getElementById(reqfields[i]);
                if(!f){continue;}
                if(f.previousSibling && /_images/i.test(f.previousSibling.nodeName))
                {
                    f.parentNode.removeChild(f.previousSibling);
                }
                f.className='';
            }
        // loop over required fields
            for(var i=0;i<reqfields.length;i++)
            {
        // check if required field is there
                var f=document.getElementById(reqfields[i]);
                if(!f){continue;}
        // test if the required field has an error, 
        // according to its type
                switch(f.type.toLowerCase())
                {
                    case 'text':
                        if(f.value=='' && f.id!='email'){cf_adderr(f)}
        // email is a special field and needs checking
                        if(f.id=='email' && !cf_isEmailAddr(f.value)){cf_adderr(f)}
                    break;
                    case 'textarea':
                        if(f.value==''){cf_adderr(f)}
                    break;
                    case 'checkbox':
                        if(!f.checked){cf_adderr(f)}
                    break;
                    case 'select-one':
                        if(!f.selectedIndex && f.selectedIndex==0){cf_adderr(f)}
                    break;
                }
            }
            return !document.getElementById(errorID);

            /* Tool methods */
            function cf_adderr(o)
            {
                // create image, add to and colourise the error fields
                var errorIndicator=document.createElement('b');
                errorIndicator.alt=errorAlt;
                /*errorIndicator.src=errorImg;*/
                errorIndicator.title=errorTitle;
                o.className=errorClass;
                o.parentNode.insertBefore(errorIndicator,o);

            // Check if there is no error message
                if(!document.getElementById(errorID))
                {
                // create errormessage and insert before submit button
                    var em=document.createElement('div');
                    em.id=errorID;
                    var newp=document.createElement('p');
                    newp.appendChild(document.createTextNode(errorMsg))
                    em.appendChild(newp);
/* added for linked list */
                    var newul=document.createElement('ul');        
                    em.appendChild(newul);
/* end added for linked list */
                    // find the submit button 
                    for(var i=0;i<of.getElementsByTagName('input').length;i++)
                    {
                        if(/submit/i.test(of.getElementsByTagName('input')[i].type))
                        {
                            var sb=of.getElementsByTagName('input')[i];
                            break;
                        }
                    }
                    if(sb)
                    {
                        sb.parentNode.insertBefore(em,sb);
                    }    
                } 
/* added for linked list */
                var em=document.getElementById(errorID).getElementsByTagName('ul')[0];
                var newli=document.createElement('li');
                var newa=document.createElement('a');
                for(var i=0;i<of.getElementsByTagName('label').length;i++)
                {
                    if(of.getElementsByTagName('label')[i].htmlFor==o.id)
                    {
                        var txt=of.getElementsByTagName('label')[i].firstChild.nodeValue;
                        break;
                    }
                }
    
                newa.appendChild(document.createTextNode(txt));
                newa.href='#'+f.id;
                newa.onclick=function()
                {
                    var loc=this.href.match(/#(\w.+)/)[1];
                    document.getElementById(loc).focus();
                    return false;
                }
                newli.appendChild(newa);
                em.appendChild(newli);
/* end added for linked list */
            }
            function cf_isEmailAddr(str) 
            {
                return str.match(/^[\w-]+(\.[\w-]+)*@([\w-]+\.)+[a-zA-Z]{2,7}$/);
            }
        }