The links to pages of other instances were only partially implemented so far. In the new version in cvs HEAD, one can link with //... to files and images in other instances in the syntax as you guessed. One can link as well to other local resources (e.g. //resources/...., or //fs/....).
Files and images are stored in the cr with a file: prefix. If this file is referenced via [[image:...]] it is rendered as image, in case it is referenced via [[file:....]] just a link is provided.
links to local labels can be achieved via [[#someanchor]]. The previous version required non-empty page names, now the page name can be left empty to refer to the actual page.
