Supplies a local path reference to a parent <animateMotion>.

DOM object: SVGMPathElement
Specification: https://svgwg.org/specs/animations/#MPathElement

href="#route" refers to a path element in the same document; xlink:href is also accepted. Changes to the referenced path data are sampled on the next frame. Missing, foreign-namespace, or non-path targets produce no motion instead of falling back to the parent's inline path. External resources are not fetched for motion references.