Ebox design

Ebox is the low-level spatial rendering engine. Its job is to turn a declarative node tree into measured layout fragments and a generic TP surface plan. It is deliberately smaller than an application framework.

Design principles

One source tree, one style normalizer, one layout pipeline, one buffer owner.
A public node is data; rendering and mutation happen only at explicit entry points.
Stable identity comes from node identity and explicit keys, never from visible text or selector strings.
Layout changes are measured before publication; a failed candidate preserves the previous buffer state.
The native module is an optional accelerator with an exact Elisp fallback.
New abstractions must remove duplication or make an existing public workflow simpler.

Pipeline

node tree
  -> normalized style
  -> measured formatting context
  -> layout fragments and snapshot
  -> render context
  -> pure TP surface plan

The owners are ebox-child-range.el for immutable child-sequence and key indexes, ebox-tree.el for Ebox identity and traversal, ebox-style.el for style semantics, ebox-measure.el for display-sensitive measurement, ebox-layout.el/ebox-flex.el/ebox-grid.el for geometry, ebox-fragment.el for fragment facts, ebox-surface.el for pure TP plan projection and retained publication, and ebox-incremental.el for dirty-owner planning. ebox-buffer-backend.el only builds and reshapes propertized render strings; all public live buffer publication routes through the TP surface boundary.

Public boundary

Use the functions and properties in docs/user/ebox-api-reference.en.md; the facade inventory is ebox-public-api. Do not call ebox--* names from an application or a sibling package. Higher-level Component, reactive, behavior, data, and control concepts belong to ETAF.

Layout scope

Ebox supports character and pixel dimensions, padding, margins, borders, colors, Emacs face/font properties, overflow, wrapping, row/column/flex formatting, and Grid tracks including fixed, fractional, implicit, gap, placement, span, and alignment behavior. The supported typography subset is :font, :font-family, :font-height/:font-size, :font-weight, and :font-slant. CSS compatibility is intentionally partial: percentages, absolute positioning, z-index, shadows, border radius, full browser typography, and browser-level bidi are outside this package.

Verification rule

Every behavior change needs a focused ERT test and a fresh make check. Changes to native source also require make native-rust-tests; changes to docs or the active file set require make docs-contract-tests.

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