OptionalchartsCharts with their cached series (best-effort; absent for .xls and when none exist).
OptionalfeaturesWorkbook-level parts the CSV dump cannot express (best-effort; absent for CSV/TSV and .xls).
OptionalpivotsPivot tables with their field names (best-effort; absent for .xls/.xlsb and when none exist).
The sheets of the spreadsheet, in workbook order.
Structural information about a parseable spreadsheet document.