Module layout 

Layout engine — positions form nodes into layout rectangles.

Implements XFA 3.3 §4 (Box Model) and §8 (Layout for Growable Objects). Supports positioned layout and flowed layout (tb, lr-tb, rl-tb).

XFA Spec 3.3 Chapter 8 — Layout for Growable Objects

This module implements the core layout algorithm described in §8.6 (p288): a content-driven single traversal of the Form DOM, adding layout nodes to a Layout DOM as content is placed into containers. When a container fills up, the engine traverses to a new container (next contentArea, next pageArea, or a new page).

Spec coverage status (reviewed 2026-04-19):

• §8.1 Text Placement in Growable Containers: ✅ implemented (anchorType via Appendix A)
• §8.2 Flowing Layout (TB, LR-TB, RL-TB): ✅ implemented
• §8.3 hAlign in various layouts: ✅ hAlign on children in TB/LR-TB/RL-TB
• §8.4 Growable + Flowed interaction: ✅ resize then reflow
• §8.5 Layout DOM structure: ✅ pages > nodes hierarchy
• §8.6 Layout Algorithm: ✅ content-driven traversal
• §8.7 Content Splitting: ✅ text-line splitting + container splitting
• §8.8 Pagination Strategies: ✅ orderedOccurrence (sequential by default)
• §8.9 Adhesion (keep): ✅ keep-chain look-ahead (keep.next/previous)
• §8.10 Leaders/Trailers: ✅ per-page leader/trailer; ⚠️ overflow/bookend
• §8.11 Tables: ✅ columnWidths, colSpan, row equalization
• Appendix A: Coordinate algorithms: ✅ anchorType (all 9 variants)
• Appendix B: Layout Objects: ✅ area, exclGroup, subformSet

Structs

LayoutDom

The output of the layout engine: positioned rectangles on pages.

LayoutEngine

The layout engine.

LayoutNode

A positioned element on a page.

LayoutNodeId

A unique identifier for a layout node.

LayoutPage

A single page in the layout output.

LayoutProfile

Per-page pagination diagnostics collected only on opt-in code paths.

LayoutProfilePage

Minimal vertical-space profiling metadata for one laid out page.

Enums

LayoutContent

Content type for layout leaf nodes.