ReadonlyresourcesBinary resources (image bytes) by id, the store pictures use. null when the value is
made outside a workbook, as an external link's cached values are.
ReadonlystringsThe string table the value's cells share. null outside a workbook.
OptionalfromThe resource a value's JSON names by id, while a file is being read: the id
IRichData.toJSON's toResourceId gave it. null for an id the file does not hold, and
always outside a read.
What a kind can reach while making a value.