Connectors
A line bound to two elements' edges that re-derives itself whenever a box moves — the diagramming primitive SVG lacks, with straight, orthogonal, and curved routes plus tinted arrowheads.
Booleans
Pathfinder-style path algebra — union, subtract, intersect, exclude — over filled regions, baked to one plain <path>; operands as children or by reference, composable with warp.
Offset (inset & outset)
Grow or shrink a referenced region by a Minkowski offset — the Offset Path / Inset & Outset operation SVG never got — with round, miter, and bevel joins, baked to one plain <path>.