Checking Margin Overflow

Margin bodies can now check their final placement against their assigned frame:

#deixis-margin-note(overflow: "error")[An explanation.]

Use #deixis-set(overflow: "error") to enable this throughout a scope. The default, "allow", preserves existing placement, including intentional overflow. A local overflow: "allow" overrides a strict inherited setting. The same option works on deixis-margin-note-body and the sidenote presets; component/type settings follow the normal body configuration cascade.

See the small two-page example.

What Is Checked

The check uses the accepted logical body rectangle after the built-in layout has chosen its side, offsets, packing, and spillover frame. A rejected provisional placement on an earlier page is not an error. Both the horizontal margin width and the vertical frame bounds are checked, with a 0.1pt tolerance for rounding. The diagnostic identifies the note and physical page and reports horizontal and vertical excess.

This works for foreground/background margin bodies and immediate layer: "flow" bodies. A flow body still stays on its declaration page, without packing or spillover. Strict overflow detects an out-of-frame body; it does not detect two bodies overlapping inside that frame. Hidden overlay notes do not claim a frame or produce an overflow error.

For scoped notes the assigned frame is the scope’s recorded margin frame. That frame does not promise clearance from native page footers or arbitrary page objects. Glyph ink, shadows, connector heads, and painting beyond a custom renderer’s logical box are outside the check.

What Happens On Overflow

"error" stops compilation when the final rectangle exceeds its frame. Shorten the body, adjust its width/offset, or provide another eligible frame for overlay spillover. The check does not create pages, clip content, shrink text, or reroute connectors. An overlarge first body or a terminal spillover body can still be accepted by the placement engine; strict mode then diagnoses that final overflow.

A custom margin-layout callback owns its output geometry. It supports overflow: "allow"; strict mode receives a diagnostic because the built-in planner cannot verify that callback’s final rectangles. Direct layout helpers without deixis-setup-notes do not run the document’s final validation pass.

The two policies keep the API compact. There is no package warning mode or silent fallback from strict checking to a different placement algorithm.