Question: questions about Maple internal software structure

I have few questions on this subject.

1) One can view internal maple procs using the command showstats. For example showstat(`dsolve`) prints the dsolve proc. And showstat(`dsolve/SERIES`)  prints the proc called  dsolve/SERIES(). And this i s what I do not understand. What is the signifcance of / in the above?    Since dsolve itself is a proc, what does / mean? does this means SERIES is an internal proc inside dsolve proc? That is not likely. I see things like convert/tan/simpler again, what does the / mean here? it can't be that simpler is an inner proc inside tan proc which is inside convert proc? I never used /  myself in mycode in a proc name.

How are these procs organized physically? I mean inside Maplesoft computers. Is each proc in separate .mpl file? How does the /  comes into play?  I tried to make a proc myself with forward / but got syntax error. So this / must mean some other logical relation, but I do not know to emulate it myself.

2) Why one must add ` ` around the names when using showstats for system procs, but not for my own module? For example, I did the following

A:=module()
  export foo:=proc()
      NULL;
  end proc;
end module;
                    
showstat(A:-foo)

And that worked. But if I type showstat(`A:-foo`)  maple gives error Error, (in showstat) procedure name expected

but with system proc, must have the `` there. If I type showstat(convert/tan/simpler) it is an error.

3) Why showstat(`DEtools/odeadvisor`)  gives Error, (in showstat) procedure name expected? But help says odeadvisor is in DEtools module.

4) Why can't one display the source of the module itself, and it has to be a proc? For example showstat(`DEtools`) gives error, because `DEtools` is not a proc, but a whole module.

Are these things described more somewhere? I only know about with(LibraryTools); 
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