You're not wrong. I put a couple links in post 18 explaining the concept.
What I'm perplexed about is this: who gives a flying fig about some nearly invisible symbolic boundary lines? Why are people so offended?
I respect the Orthodox Jews but, truth be told, it wouldn't make any difference to me if it was Hindus, Mormons or Santeria. It's an invisible boundary line that helps innocent, blameless, inoffensive people have a little more freedom of movement and action on the Sabbath.
Seriously, have at it. What's not to like?