I would also like the ability to add a note to a cell. I want to provide more context to the user about the value returned by a custom function. For example they used a custom function to request the Market Cap of MSFT on 12/31/23, but 12/31/23 was not a trading day, so the function has returned the Market Cap of MSFT on 12/29/23, the last trading day before 12/31/23.
It would be great to be able to use something like the https://learn.microsoft.com/en-us/javascript/api/excel/excel.formattednumbercellvalue?view=excel-js-preview, https://learn.microsoft.com/en-us/javascript/api/excel/excel.cellvalueattributionattributes?view=excel-js-preview, or https://learn.microsoft.com/en-us/javascript/api/excel/excel.cellvalueproviderattributes?view=excel-js-preview interfaces. For example a `note` property to attach a note to the cell when the function returns a value to the cell.