Plane Geometry

The conventions every two-dimensional surface shares, as pure maths: pointer to plane fractions with y read bottom-up, the keyboard step where the plain arrow is coarse and Shift is fine, clamping to a point's own limits and snapping to the axis step, directions in degrees (0 along +x, counter-clockwise) that wrap on a full turn, first-order polar patterns from omni to figure-8, nearest-point picking within a radius, and grid lines by spacing or divisions. XYPadHeadless and PlanPad both read it, so one point and N points cannot disagree.