PHP reloading scripts without reloading the page

[bokeh]

Would this work across websites, like say if I my domain were example.com and I had a user who wanted to use it on foo.com, could I tell him to put

<script type="text/javascript" src="http://example.com/analytics.js"></script>

in his HTML document?

No, no decent browser would allow it. When using the XMLHttpRequest object the requested document must be on the parent domain.