CSS formatting tree, Flexbox and Grid algorithms

Document status: reviewed. Canonical source.

Summary

CSS separates the source element tree from an intermediary formatting box tree and then applies family-specific layout algorithms. CSS Display defines box-tree generation; Flexbox and Grid define normative algorithms whose results implementations must reproduce even if their internal algorithms differ.

NUIF relevance

This strongly supports separating semantic containment from formatting/layout structure. NUIF can borrow exact CSS-compatible semantics where selected, but should not claim arbitrary HTML/CSS equivalence when anonymous boxes, generated content, cascade, writing modes or other web-specific fixups are absent.