function clearTextBox(txtInput)
    {
        if(txtInput != null && txtInput.value != null)
        {
            //console.log("value = %s", txtInput.value);
 
            if(txtInput.value + "" == "vas.email@domena.cz")
                txtInput.value = "";
        }
    }
 
    function fillEmptyTextBox(txtInput)
    {
        if(txtInput != null && txtInput.value != null)
        {
            if(txtInput.value + "" == "")
                txtInput.value = "vas.email@domena.cz";
        }
    }
 
    function checkEmail(checkedForm)
    {
        //sconsole.log("value = %s", "submitting");
 
        var txtEmail;
        var error_msg = "\tJe třeba zadat email ve formátu\n\tvas.email@domena.cz\n";
        var filter = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;        
 
        if (checkedForm != null && document.getElementsByTagName)
        {
            /* =====================================================================
             * Inputs of the form
             *====================================================================*/
            var vInput = checkedForm.getElementsByTagName("input");
            for (var vCount=0; vCount < vInput.length; vCount++)
            {
                if(vInput[vCount].type == "text")
                {
                    txtEmail = vInput[vCount];
                }
            }
 
            if(txtEmail != null && txtEmail.value != null)
            {
 
                if( (txtEmail.value + "" == "") || (txtEmail.value + "" == "vas.email@domena.cz") || !filter.test(txtEmail.value) )
                {
                    fillEmptyTextBox(txtEmail);
                    alert(error_msg);
                    txtEmail.focus();
                    return false;
                }
                else
                {
                    return true;
                }
            }
        }
 
        return false;
    }