You got me going down the right path, thanks.
[[++site_url]][[~[[*id]]]]
... will generate the full furl of the page at hand.
These are being used as hidden inputs for forms, for social media posts, for display purposes, etc. We want the full friendly url to be seen, because they are more indicative of what the webpage is about and because they are more SEO beneficial since they point to the same urls gathered by search engines. To switch back and forth between resource ids and furls would be problematic for outsiders.