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	Models/emits styles, row/column layout, merges, date1904, view/zoom/frozen panes, dynamic-array metadata, and supported tokenized formulas. Existing worksheet tails are preserved verbatim.
.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 saveAs / save_as in the bindings) and sniffs content on read, so a .xlsb-named file with OOXML bytes (or vice versa) is still handled correctly.

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.