There are several references on this forum to modifying a page's behavior by placing html of the following form in the body of a page:
<script type="text/javascript">xr_v1(document.getElementById('message ').parentNode.parentNode)</script>
Although I've following the "instructions" for using it, I have seen no evidence that it actually works or is even executing ... which leads me to these questions:

Is there a statement I can add to that block that would display a message or change a color ... or something?
xr_v1 appears to be a function. Where might I find it documented?
When such a script is in the body html, when is it executed?

As you can tell, I'm not versed in javascript. And it's tough to get even a toehold when viewing resources like W3School. But I'm trying to learn.

Thanks in advance for any assistance.