Michal,
CR items are not mounted like package instances. In OpenACS CR items are objects within the database which, though often associated with and exclusive to a package, may not necessarily be.
For example, a photo in the photo album package is stored in the CR and can be retrieved independently of the photo-album package. This is done with a URL to the content item that is handled by the request processor itself, and is sometimes useful.
However, the proc you have asked about is a deprecated proc see below:
http://www.openacs.org/api-doc/proc-view?proc=item%3a%3aget%5furl
I hope that this is of some help.
Richard
