For a cross-frame page link, src-frame-side / dst-frame-side and
src-frame-anchor / dst-frame-anchor select the invisible outer page side and
its tangent slot independently from the item anchor. The actual terminal moves
only along the inward normal to a parallel inset line: resolved metadata
row-gap, or 4 layout pixels without metadata; zero remains on the outer edge.
The complete cross-frame page-link example
demonstrates different endpoint and page-edge sides at both ends.