When dragging an item from DEVONthink, $URL is set to the DEVONthink item URL if it has once. For example, if the item is a web page, $URL is set to the URL of that page. If the item doesn’t have a URL, Tinderbox sets $URL to the DEVONthink internal URL to allow prompt reference to the item.
More on interactions with DEVONthink.
See also—notes linking to here: