Clarifying what does and does not get mirrored in a Push Mirror

Where can I get some clarity on what does not get mirrored in a Push Mirror. For instance do Variables get mirrored ?
A/- Is there a list or document that clarifies this?
B/- Is there any control to what does and does not?

Cheers
Rusty

(I am relatively new to GitLab. I have being thrown in the deep end :smiley: and need to come up to speed fast while I try to do some study on the back side)