function addText(obj)
{

if(obj.value == '')
    obj.value = "zip code"; 
}

function clearText(obj)
{
if (!(obj.value > 0))
obj.value = ""; 
}

function isValidTextLength(control, textLength)
{
    //verify the empty field.
    if(document.getElementById(control).value == "")
    {
        alert("Please write the text to add.");
        return false;
    }    
    else if(document.getElementById(control).value.length >= textLength)
    {
        alert("More than "+textLength+" characters are not allowed.");
        return false;
    }
}