Ideas

Things the design would accommodate but that nobody has asked for yet. No promise — this file exists so an idea worth half an hour of thought is not re-thought from scratch in a year. Where one has become an issue, its entry says so.

An entry is deleted when it is built, or when it stops being a good idea.

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Say whether a sheet is hidden

A workbook marks sheets state="hidden" or state="veryHidden" — lookup tables, scratch space, a template's internals. The cursor lists them like any other sheet, which is the right default: hiding is presentation, and the data is still there. Sylvan.Data.Excel skips them instead, which is how the comparison in #8 noticed.

What a caller cannot do today is tell them apart. A mapping screen offering "which sheet?" should probably show the visible ones first, or mark the others. SheetInfo would carry a Visibility (Visible, Hidden, VeryHidden) read from the same <sheet> element the name comes from — no extra part, no extra cost. A csv's single sheet is always visible.