The arrows stand-in image for the editor stage's sample-values mode — a light-gray square with four arrows radiating to the corners and a "Placeholder image" caption, shipped as a data:image/svg+xml URL.

Browser-only. The stage is a real DOM, and browsers render nested SVG data URLs fine. Rasterizers don't (nested-SVG <image> support varies — the original "black square" bug), so this value must never reach the PNG pipeline: the preview pane and the public render keep OpenFresco's labeled stand-in for unresolved image slots.