Pointer-capture drag for SVG/HTML handles. On pointerdown captures the
pointer, then forwards every pointermove to onMove with coordinates
local to the rect-providing element (defaulting to the handle's owning
<svg>). Listeners are cleaned up on pointerup / pointercancel.
Pointer-capture drag for SVG/HTML handles. On
pointerdowncaptures the pointer, then forwards everypointermovetoonMovewith coordinates local to the rect-providing element (defaulting to the handle's owning<svg>). Listeners are cleaned up onpointerup/pointercancel.