# XLSX Round Trip Foundation

SheetJS CE is used for worksheet values, formulas, merges, dimensions and basic styles.  UnifiedSpread-native metadata that cannot yet be expressed reliably through SheetJS CE is preserved through a hidden worksheet named `__UnifiedSpreadMetadata`.

The hidden metadata sheet stores:

- workbook config, including named ranges and collaboration metadata;
- per-sheet config, including filter, validation, conditional formatting and pivot metadata;
- floating object metadata for charts, images, shapes and text boxes.

This does not claim full Excel OOXML fidelity.  It provides a practical round-trip bridge until dedicated OOXML writers for comments, drawings, chart parts and pivot caches are added.