How making noise for anything but the direst emergency should be an off-by-default privilege that only the user can explicitly grant, instead if being the default for all electricity-powered objects.
If you're designing objects, please take some time to test their notification mechanism near an asleep toddler and/or a sleep-deprived lunatic, instead of making piling more noisy interruptions to our already notification-saturated reality.
A PDF file is effectively a graph of objects that may reference each other. Objects reference other objects by use of indirect references.