QStandardItem's header item and header label

What's the difference between header label and header item?
Is the header label or header item a part of a row or column(removing a row or column will also remove the header, so the header should be taken as a special item of column)?
Furthermore, appending column to a empty table with vertical headers will append after these headers. Is it possible to change such behavior?

Header item is a QStandardItem representing the data returned by QAbstractItemModel::headerData() and used by QHeaderView in views. A header label is a convenience variable representing the header item's text property.