function canAddCharacter(textarea, maxChars)
{    
    if(typeof(textarea.onkeypress.arguments[0]) != 'undefined')
        var keyCode = textarea.onkeypress.arguments[0].keyCode;
    else
    {
        if(document.selection.createRange().text.length != 0) return true;
        var keyCode = event.keyCode;
    }

    var allowedChars = new Array(8, 37, 38, 39, 40, 46);    //Backspace, delete and arrow keys
    for(var x=0; x<allowedChars.length; x++) if(allowedChars[x] == keyCode) return true;

    if(textarea.value.length < maxChars) 
    {
        return true;
    }

    return false;
}

function trimLength(textarea, maxChars)
{
    if(textarea.value.length <= maxChars) return;

    textarea.value = textarea.value.substr(0, maxChars)
}

function update (name, maxchars) {
    var c = document.getElementById('contador');
    if (typeof c == 'undefined') { return; };
    
    c.value = document.getElementById('cuerpo').value.length 
            + '/' 
            + maxchars;
}