function isPositiveInteger(s)
{   
    if (s == "") return false;
    for (i = 0 ; i < s.length ; i++) {
        if ((s.charAt(i) < '0') || (s.charAt(i) > '9')) 
        return false
    }
    return true;
}

function insertAfter( referenceNode, newNode )
{
    referenceNode.parentNode.insertBefore( newNode, referenceNode.nextSibling );
}
function validateForm()
{            
    var people_from  = document.forms.advanced_search.people_from;
    var people_to  = document.forms.advanced_search.people_to;
    
    var valid  = true;
    var error = "";
    
    if (
        ((people_from.value.length != 0) && !isPositiveInteger(people_from.value)) ||
        ((people_to.value.length != 0) && !isPositiveInteger(people_to.value)))
    {
        document.getElementById('error1').style.display = 'block';
        valid = false;
    }
    else
    {
        document.getElementById('error1').style.display = 'none';
    }
    
    if (isPositiveInteger(people_from.value) && isPositiveInteger(people_to.value) && (Number(people_to.value) < Number(people_from.value)))
    {
        document.getElementById('error2').style.display = 'block';
        valid = false;
    }
    else
    {
        document.getElementById('error2').style.display = 'none';
    }
    return valid;
}