If you want to make an AJAX call from your browser to fetch some HTML from your server and put that data inside a div, you don't need to use JSON for that. Just have your Arc op return the HTML.
Untested, so I apologize for any mistakes:
(defop grabdata req
(pr "This is my <i>HTML</i> content!"))
and, in the browser, using for example JQuery (http://jquery.com/) as a convenient way to make the AJAX call:
$.get("http://yourserver.com/grabdata", function (data) {
$('#your_div').html(data);
});
replaces the contents of the div that has the id "your_div" with the HTML content returned by grabdata.
