It's worth trying Inventor (or Autodesk Fusion 360, which is basically a cloud-based Inventor with a free demo) to see a constraint system with a good GUI. Draw lines and make boxes, and if you end a line at an edge, the line endpoint is constrained to that edge. End a line at the endpoint of another line, and those points are constrained to be at the same place. If a line is drawn vertically or horizontally, it's constrained to stay vertically or horizontal. Drag a point or line, and everything else is adjusted, but as little as possible, to maintain the constraints.

Specify that two lines must be parallel, or perpendicular, or the same length, and those become constraints. Specify a dimension between two lines or points, and they stay that distance apart. A dimension can have an expression based on other dimensions, so if you need something to be twice the distance of something else, you can do that.

This goes beyond straight lines. You can have a circle or arc constrained to touch a line or another circle or arc. A curve can be constrained to be tangent to something else, for a smooth transition. Designers would love that.

The GUI won't let you add a constraint that conflicts with another constraints. There's no "constraint priority". All constraints are equal.

The GUI has a counter which shows how many degrees of freedom still need to be constrained. Little red arrows show you what can still move. When everything is constrained and nothing can move, the counter changes to "fully constrained", and the sketch is now rigid. But you don't have to go all the way to fully constrained if you don't want to. The system will do something reasonable if you don't.

Some sketch dimensions may be driven from another sketch. In the web world, this would correspond to adjusting to window size.

The CAD people deal with hard geometry problems, much harder than the ones web layouts face, and they have much better technology for doing it. It's even user-friendly.