Membrane detail 2d

How would you even go about making a definition that creates such a ‘line pattern’ around an input curve?
It is a standard way of representing membranes in 2d details.
I struggle to imagine how to create boundaries for these black hatches.

I was so surprised that it worked for me for after first try lol.
Have a bad habit of posting too early

I had to do something very similar but in a completely different context

in my case a requirement was for the very first and very last pattern along each curve to be the same (in your case it would mean to always start/end with hatch / with non-hatch)

in case it might look useful this is the part that goes to the offset (instead of divide by Length): it makes the number of segments the curve is divided into an always-odd number