Noob question

In the sesi documentation it suggests to use __PDG_DIR__ instead of ${PDG_DIR} for filename paths.

ok, I tried and only received errors in the graph when cooking ROP Geo Output.
No issues if I use $JOB or $HIP instead.

That's the first issue

2nd is a noob question on proper use of environment variables in TOPs

What is the difference between

${PDG_DIR}

$PDG_DIR/

and

__PDG_DIR__ ?

I'm on Linux (Ubuntu 18.04LTS)