[andiwand]

🤖 Generated with Claude Code

Refs #764.

Summary

This adds decision 6 to docs/design/lazy-loading.md: a sheet at level 1. content-visibility has no effect on a tr or a tbody, so a chunk of a sheet is a <table> of its own.

• Wrapper: a div.odr-sheet takes the attributes that table.odr-sheet states today. Rules of the form .odr-sheet td stay as they are.
• Ruler: a sticky thead sticks only inside its own table, so the column letters get a sticky table before the chunks. The row labels stay sticky at the left in each chunk.
• Column widths: every table has table-layout: fixed and the same colgroup. A column that states no width, for example in a csv, sizes by its content today, so each chunk would size it differently. The writer gives such a column the width of its longest text in the first 1000 rows, in ch, from 4 to 60.
• Chunk boundaries: at most 256 rows or 4096 cells, at least 8 rows, and a chunk ends only where no rowspan is open.
• Height: each chunk states the summed height of its rows as contain-intrinsic-height: auto. A wrapped row corrects itself on first layout. Safari may lack scroll anchoring, so the page there can move by the error of the estimate.
• Shapes: a shape hangs from A1, so the first chunk of a sheet with shapes stays near.
• Scripts: a table lists each read of the rows and of the geometry, and how it works with chunks. This covers the row accessor, the sort, row and column edits, the deferred reflow of a hidden chunk, the selection overlay, the pin through odr.chunks.show, and the formulas.
• Limits: they stay as they are in this step.

Level 2 of a text file drops out of the order of work. When measured, it gained little over the hidden chunks.

Review fixes

• Rebased onto main after the squash of feat(html): lay out only the pdf pages near the viewport #1248. The order of work had a conflict with the counter sentence of docs: design lazy loading in three levels #1246. The rebase keeps that sentence and the new item 2 of this PR.
• The status said that nothing of the design has landed. It now says that level 1 has landed for text files (feat(html): lay out only the lines of a text file near the viewport #1247) and pdf (feat(html): lay out only the pdf pages near the viewport #1248).
• The script table said that viewport.js "raises odr-chunk-near" when a chunk becomes near, which is the name of the class. A class change tells no script, so the table now says that viewport.js dispatches an event on the chunk.