File Format Support
Summary
Read, write, and preserve are separate concepts
Read means Formulon can parse the structure. Write means it can emit it. Preserve means it can carry it through a round-trip. Only evaluated features affect calculation.
| Area | Status |
|---|---|
.xlsx read | Implemented for workbook, sheets, cells, styles, shared strings, relationships, tables, names, comments, hyperlinks, merges, validations, conditional formatting, pivot structures |
.xlsx write | Writes back everything the read row above lists — workbook, sheets, cells, styles, shared strings, relationships, tables, names, comments, hyperlinks, merges, validations, conditional formatting, and pivot structures — as part of recalculated workbook output |
.xlsb read/write | Cell values, formulas (including cross-sheet 3-D references, LET and other future-function names, and dynamic-array spill formulas), and styles round-trip. Conditional formatting, pivot tables, comments, and data validation are still OOXML-only; array-constant literals are limited to numeric elements |
.xlsm macro bytes | Preserve, never execute |
Legacy .xls | Out of scope |
| Charts/drawings rendering | Out of scope |
| Pivot cache recomputation | Out of scope; structure preservation is in scope |
Formulon picks the container format from the output file extension (-o file.xlsb on the CLI, or saveEx / save_ex in the bindings) and sniffs content on read, so a .xlsb-named file with OOXML bytes (or vice versa) is still handled correctly.
Recent round-trip updates
The v0.9.1 and v0.9.2 releases jointly tightened preservation for workbook relationships, shared-formula reference shifts, and print pagination metadata: v0.9.1 introduced round-tripping for page setup, margins, header/footer, print options, and opaque printer settings, and v0.9.2 closed residual cases and added oracle-side pagination-margin capture. That round-trip path remains part of the supported surface for modern .xlsx workflows.
The v0.9.3 release closed the major .xlsb protocol gaps reflected in the table above: style records, workbook-scope names (including LET and other future functions), cross-sheet 3-D references, and dynamic-array spill formulas. Several of these previously produced .xlsb files that real Excel could not open.
The v0.9.4 release round-trips data-validation dropdown visibility (show_dropdown) through OOXML. Excel stores this as an inverted showDropDown attribute, so Formulon exposes the host-facing show_dropdown meaning while preserving the file-format semantics on read/write.
Preservation rule
If Formulon does not semantically own a workbook feature, the preferred behavior is to preserve the package structure where practical. This lets Formulon update values while another tool owns authoring, rendering, or review.
Calculation rule
Only features represented in the calculation engine affect recalculation. Preserved structures are not automatically interpreted.