Type: string Scope: Display / Proc.
Define a field on the child record (or on the intermediate table) that stores the manual sorting information. It is possible to have a different sorting, depending from which side of the relation we look at parent or child. This property requires that the foreign_field approach is used.
If you use the table only as an inline element, do not put the sortby field in the ctrl section, otherwise TYPO3 CMS will sort the entire table with every update. For example, if you have 10000 records, each with 4 inline elements, TYPO3 CMS will sort 40000 records even if only 4 must be sorted.