Insert the referer, if available: The Referer field allows the
client to specify, for the server's benefit, the address (URI) of the
document (or element within the document) from which the Request-URI
was obtained.
This tag can be used for making a 'back button', that's a link
back to the page he just was on (I use it for the [BACK] button in
this documentation). It's recommended to use it together with <if referer>.