Demonstration of SVG marker refX is not arc-length aware

svg-refx-not-arclength.svg

<svg width="460" height="200" viewBox="0 0 460 200"
     xmlns="http://www.w3.org/2000/svg">

  <defs>
    <!-- Small arrow marker -->
    <marker id="arrow"
            viewBox="0 0 10 10"
            refX="0"
            refY="5"
            markerWidth="8"
            markerHeight="8"
            orient="auto">

      <!-- HUGE refX sweep while marker stays tiny -->
      <animate attributeName="refX"
               values="-40; 40; -40"
               dur="3s"
               repeatCount="indefinite" />

      <path d="M0,0 L10,5 L0,10 Z" fill="black"/>
    </marker>
  </defs>

  <!-- Curved path -->
  <path d="M40,150 C150,10 310,10 420,150"
        fill="none"
        stroke="black"
        stroke-width="4"
        marker-end="url(#arrow)" />

</svg>

This demo animates a small arrow marker’s refX across a large range on a curved path.
The arrow visibly detaches from the endpoint instead of sliding along the curve, proving that:

refX is applied as a simple post-translation in marker space after orientation is solved,
not as a geometric movement along the path’s arc length or local frame.