Can PHP detect a referrer of another protocol?

[Mr Initial Man]

I know you can do something like "$_server['HTTP_REFERER];" and get the website that the referring link was in. But what if you're using a different protocol What I am trying to do is have a MySQL query run when AND ONLY WHEN a link was clicked from the Furcadia client (which uses the furc:// protocol), instead of a URL being entered directly or someone clicking on a link in a webpage. Basically, the referring URL would be furc://puzzlepalace.

Is this even possible?

[Derokorian]

While would be possible to get the protocol from the referrer, this is a header provided by the browser at its own whim (aka no guaruntee its there, or accurate). On top of that the user would be clicking a link in another program, meaning as far as the browser knows there is no referrer to populate (its the first page visited in that tab/window). What you could do it give a query string value to the URLs appearing in said third party program, and check for its existence.