[nrclark]

re 1 and 2: awesome! I'm excited and will be trying out Horizon my next design.

re 3: I was more thinking about the plane spacing. Like say I'm making a board where I want to carry a high-speed clock signal. If it's single-ended, chances are the transmitter has a 50-ohm output impedance, and the receiver has a 50-ohm input impedance.To get the cleanest signal, I want my trace to have a 50-ohm _characteristic_ impedance (which is a function of the trace-width, distance to the closest plane layer, and PCB substrate's chemical properties).

Trying to model it accurately is a huge pain in the ass, and probably not worth attempting. But it could be nice to have a rule-checker that says something like "for your PCB dielectric constant of 4.7 with 10mil spacing to the nearest plane, your trace should be 18mil wide to get the desired impedance".

There are a bunch of these calculators out there - but it would be super cool to do some rudimentary constraints as DRC!