Some packages, such as general-comments, search, notifications, need to be mounted per subsite. One reason for this is if the host-node map is used and you want the service user interface to appear under the correct subsite URL.
It also makes it easier to manage parameters on a per-subsite basis.
Right now you can mount a singleton package more than once, but this has problems.
I think it would be useful to have a way to specify that a package may be mounted once per subsite, or subsite-like package as specified by apm_packages.subsite_p. This way it would be possible to calculate the package_id, node_id, and url of a service package like general comments, for the closest subsite, or subsite-like package instance.
Unless someone has a better plan, I think adding a subsite_singleton attribute to the .info file would work. The APM would need to check that a package only existing once in an immediate subsite. That is, nested susbsites would still be allowed to have once package instance per subsite. I'll submit a TIP incorporating any suggestions.
On a related note, I think we should set dotlrn as a subsite_p=t package so that it will be easier to reuse code for subsites in dotlrn communities. I'll start a second thread around this.
