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We start with a mockup of the humidifier example:
SysPhS-1.1: 'A.5.2 System being modeled: The total humidifier system has two main components: the humidified room and the humidifier, see Figure 64. The humidifier uses information about the room’s humidity level to determine how much vapor to input to the room. The humidifier includes a water tank, a heater controller, and a vapor generation plant.'
This is not a screenshot of the spec document figure, it's actually been redone in a drawing program, and includes a tiny bit more detail than the spec figure.
The spec figure does seem to imply that part of the humidifier is exposed to the room (and thus the room temperature) while part of the humidifier is exposed to the external environment (and thus its temperature).
We'll see next how this is represented in an Internal Block Diagram (IBD) - after some substantial detective work concerning units has already been done.