Ability to Assign Custom Properties or Unique IDs to Individual Cells

Summary
I'd like to request support for assigning custom metadata — such as unique IDs or arbitrary key-value pairs — directly to individual cells in Excel using the Office.js API.

Why This Matters
Currently, developers must rely on workarounds like named ranges, hidden metadata sheets, or cell notes to simulate per-cell identifiers. These approaches are either limited, fragile, or not scalable for large applications. Native support for cell-level metadata would unlock powerful use cases:

• Dynamic form builders
• Cell-level validation engines
• Workflow tracking
• Data lineage and audit trails
• Integration with external systems via stable cell references

Proposed API Concept

range.customProperties.add("id", "cell_001");

const id = range.customProperties.getItem("id").value;

Or even:

range.metadata = {

  id: "cell_001",

  status: "approved",

  validator: "admin"

};

Benefits

• Eliminates reliance on fragile naming conventions
• Enables scalable, structured metadata management
• Improves developer experience and app robustness

Alternatives Considered

• Named ranges: limited and global scope
• Notes/comments: visible to users, not structured
• Hidden metadata sheets: hard to maintain
• Custom XML parts: complex and not cell-specific

Request
Please consider adding support for cell-level metadata or custom properties in a future version of Office.js. Even a lightweight key-value store per cell would be a game-changer.