Rows before the first header are parsed by a layout inferred from those rows
(the header's indices may not match them); the header is written first.
Without any header the layout is inferred from all rows and a header with
code and name and empty period texts is created. Value columns: amounts
outnumber junk or the column is fully empty.
Refs #6
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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