从php文件运行.innerHTML以更改HTML元素

I'm an old school RPGILE programmer trying to create a website. How do I get .innerHTML working from a PHP file (with HTML embed) to change an HTML element text?

My PHP (file) code:

$txt = 'First Name is required!';
sInnerHtml($reginfo, $txt);    
// $reginfo is the name of the HTML element

sInnerHtml points to a (PHP file) service function:

function sInnerHtml($element, $text)
{
echo <<<_END
<script>
    jO("$element").innerHTML = "$text"
</script>
_END;
}

jO points to a JavaScript alias:

function jO(obj)
{
    if(typeof obj === 'object')
        return obj
    else
        return document.getElementById(obj)
}