Can Time Capsule backup its own network share or can Time Machine be setup to do so?

Can Time Capsule backup its own network share or can Time Machine be setup to do so?

Apple's Time Capsule can act as both a backup drive and a network shared drive at the same time. Can it backup its own data to incremental backups? I can't find this information anywhere. I've not used Time Machine so I don't know if it can be configured to backup shared drives (independently of whether Time Capsule has the option).