Variable names in error messages: How to interprete the name of a variable for where it is defined and what does it define?

I got an error message:" The source selection for the operator root.comp1.solid.cnt1.max_dst must be nonempty.Error in multiphysics compilation."

How can I interpret this message?
How can I know, where this variable is defined?

I presume, the dot separate different states and nodes
root. = ??
comp1. = .. I presume the compiled geometric object is meant?
solid. = I presume a solid mechanics module does the definition???
cnt1. = ???
max_dst = ????