For runtime introspection.
Return copyable items that are not cells.
The source range
Scan the values of the source range
Optional
options: CellVisitorOptionsScan any columns.
Optional
options: CellHeaderVisitorOptionsScan any rows.
Optional
options: CellHeaderVisitorOptions
Useful for when we are not copying from the current sheet. This abstraction exists to allow for custom sources such as a clipboard.
Remarks
There is a default implementation SheetCopySource that can be used to copy between sheets.