< and > should be escaped/encoded in <div class='runtime'>
After saving a record via edit.php, I can see a <div class='runtime'><span class='rusage json'>
element right at the end of <body>
which contains a json object. The element is not normally visible, but viewing the page source confirms that it is present.
However, if one of the fields in the record that was updated contains an HTML tag (or perhaps any `presence <
or ```>``` chars; I haven't experimented fully) then they get included verbatim in the HTML. This ultimately leads to a kind-of broken HTML document, which includes some part of that json object being shown at the end of the page (screenshot is truncated; there's plenty more json afterwards)
I suspect the fix is probably to wrap whatever is producing the json within <div class='runtime'>
in htmlentities(), or something to that effect, though I don't know what the intended purpose of that element is.