I'm developing an app that will offer the ability to chatter - i.e. automatically generate chatter posts based upon events within the application. This functionality will controlled by a setting within the app allowing users to turn it on or off.

It is important that this app can be successfully installed into an org whether it has Chatter enabled or not. The idea being that if the user has chatter enabled they are able to set the application to automatically generate chatter posts but if they don't have chatter enabled, the application will install and run without any issues.

I notice on package upload, under the package requirements section, chatter is now automatically selected. But it is possible to deselect it. My question is:

What happens if the Chatter package requirement checkbox is deselected (while the package contains apex that refers to Chatter objects), will the install still fail on an org that does not have chatter enabled?

Can a package that contains apex references to Chatter objects be successfully installed into an org that does not have Chatter enabled?

Obviously answers to these questions can be determined by some trial installations but it would be very useful indeed to get some answers from someone with knowledge of this area.

Thanks