>>I've never heard of "Mom's rule". What is that?
>
>"If you use it - put it back the way it was"

Also can be said: "leave things the way you found them."

The first time I saw this rule stated for the programming standard was on the Universal Thread a week or two ago ... I loved it, I grabbed it right away. It appeals to me more than the older term: "black box code".

(For you younger programmers, "black box" refers to a function/subroutine that is like a black box machine. You don't have to know what's inside. You put something in, it gives something predictable back, and it doesn't change anything that's outside of itself.)