Suggestion: DDI → XLSForm tab (formtransform ddiToXlsform)

[jstet]

Suggestion, not planned yet.

Since formtransform v0.7.0 (#154, #160), the library has ddiToXlsform(xml, { onWarning }). It turns DDI-Codebook 2.5 XML back into an XLSForm and runs in the browser. The app could offer it as a fourth tab, "DDI → XLSForm".

What the library gives

• ddiToXlsform(xml, options?) → { survey, choices, settings } (sheet rows, XlsformOutput).
• It reads a whole codebook, a dataDscr, or bare var / varGrp elements, and never refuses DDI it can parse.
• A CDL codebook (written by this app's Kobo tab or by xlsformToDdi) comes back exactly. The library round-trip tests DDI → XLSForm → DDI byte for byte.
• DDI from other tools converts as far as its standard elements go, with a ddi-field-missing warning per field it can't supply.
• Still lost: unregistered types such as calculate, and a few cell spellings (src/pipelines/ddi2xlsform/README.md in the library).

What the app would need

• A Ddi2XlsformTab.svelte: file input for .xml, Convert, download form.xlsx, and an optional preview of the survey sheet.
• Writing the three sheets to .xlsx with SheetJS, which is already a dependency (xlsx). Keep the column order the library returns.
• Warnings through the existing ErrorBox (warnings prop). They matter here: DDI from other tools produces ddi-field-missing findings the user should see.
• i18n strings (DE/EN) for the tab label, file label and hint.
• A short line in the scope notice or the tab: exact round trips only for CDL codebooks.

Tests

• Golden: for every ddi.xml in the fixtures archive (registry types and survey fixtures), upload it and compare the downloaded workbook's sheets with the library's own ddiToXlsform(xml) output.
• Round trip through the GUI: Kobo tab → survey.xml → DDI tab → form.xlsx → Kobo tab gives the same DDI.
• GUI: a non-CDL DDI fragment converts and shows ddi-field-missing warnings.
• Accessibility: add the tab to accessibility.spec.ts.