paginate: cut a laid-out document into pages under CSS fragmentation - #142
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A new pure-logic package: Breaks(root, pageH) / Paginate(root, Options) return the document y at which each page after the first starts. It cuts only between atoms — a text line, a whole table row (a layout-table wrapper row is descended into), a leaf box with height — the rule go-pdfkit/html2pdf paginated with, moved here so every consumer of the layout tree paginates alike; and it now reads what the document asks (css #141): forced breaks (break-before/after: page, left, right and the page-break-* aliases), break-inside: avoid kept whole when the box can fit a page, break-before/after: avoid (keep with the next or previous content), orphans and widows — relaxing orphans/widows first and the avoid rules second when a page cannot otherwise be cut, as css-break-3 §5.4 prescribes. Margins adjoining an unforced break are not truncated (documented). The answer key is Chrome: html2pdf's fixture (sections, a straddling table and figure, a heading kept with its paragraph, an eight-line paragraph with orphans/widows 3, on A5 with 15 mm margins) printed with headless Chrome gave marker → page; laid out at the A5 page area with the engine's own fonts, every marker lands on Chrome's page and the count is Chrome's nine. Synthetic trees cover each rule and each relaxation. 100 % covered and added to the coverage gate at 100. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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What
New package
paginate(pure logic, 100 % covered, gated at 100):Breaks(root, pageH)/Paginate(root, Options{PageHeight, FirstPageHeight})return where each page after the first starts. Atoms are text lines, whole table rows (layout-table wrapper rows descended into) and leaf boxes with height — html2pdf's rule, moved here. It now honours the document's CSS fragmentation (#141): forced breaks (page/left/right,page-break-*aliases),break-inside: avoid(kept whole when the box fits a page),break-before/after: avoid(keep with next/previous),orphans/widows, with css-break-3 §5.4's relaxation order when a page cannot be cut otherwise. Documented limit: margins at an unforced break are not truncated.Measured against Chrome
html2pdf's
corpus/fixtures/breaks.html(sections withbreak-before: page, a table and a figure withbreak-inside: avoidplaced to straddle a page end, anh2withbreak-after: avoid, an eight-line paragraph withorphans/widows3;@page { size: A5; margin: 15mm }) printed with headless Chrome 141 gave the marker → page key. Laid out at the A5 page area (118 × 180 mm) with the engine's fonts,paginateputs every marker on Chrome's page and produces Chrome's nine pages (the orphans paragraph is cut with ≥ 3 lines each side, as the constraint says; Chrome cuts 4 + 4).Tests
Synthetic trees for plain fill, forced breaks (short page), avoid-inside kept whole / cut when taller than a page, keep-with-next in both forms, orphans/widows (3/3, 4/4, unsatisfiable 5/5 relaxed), a chain of avoids longer than a page, tall atoms overflowing, first-page height, wrapper rows, nil/empty — plus the Chrome answer key.
🤖 Generated with Claude Code