DTM: Writing Custom Condition for Page Load Rule

I can't seem to find any documentation on the form that the custom script needs to be written for conditions on the page load rule. I'm trying to write a page load rule for my error page to set the pageType=error page. The rule is not loading at all from what I can tell. When I put the code from the condition into my console, I can see that my variable "myBool" fires as true, so my code is correct (I think!)

For the condition, I am basing it on our H1 tag to identify the page (triggered at bottom of page):

is404 = function () {

    var myBool = false;
    var myH1 = document.getElementsByClassName("hero-title")[0].innerHTML.toString();
    if (myH1 == "The information you are trying to access has moved." ) {
        myBool = true;
    }
    return myBool;

}
is404();

Then in the rule portion for Adobe Analytics, I am setting the custom page code to:

var s= window.s||s;
s.pageType=errorPage;