Translate cross reference to a link

['Rowan Goemans' via sphinx-dev]

In an extension I want to make use of existing references and allow a user
to cross reference. The plugin in question outputs svg so directly keeping
the ref in the result won't work. So what I want to do is translate an rst
fragment to the form it would represent in the output. For instance if I
would pass `google <www.google.com>`_ It would the return the correct
format for the output specified. The same should work for using roles or
domain references. This is done so I can then substitute the rst in the svg
and put in the actual link. I can't find how to do something like this.
Even reading parts of the builder source code I can't see how I can do
this. I hope somebody can push into the direction how I can manage
something like this.

Regards, Rowan Goemans