Layer Kes vers System Definitions

[Anonymous]

Can someone please clarify the difference between Layer keys, and System
Definitions?

I've created new Style based content for nurse call devices. I've assigned a
specific layer key for each block.

In my template file, I have system definitions for nurse call devices. When
you insert devices in a project, you give it the system, which in turn
over-rides any layer key you've defined within the block!!! How do these
relate? What is the intent of defining layers via systems, verses defining
layers via specific devices. Can someone please shed some light!!! I'm
missing the picture, and need clarification.