Display / Proc.
Define a field on the child record 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.
Do not confuse this property with foreign_default_sortby. The
foreign_sortbyfield contains an integer and is managed by the DataHandler. If by accident a content column like "title" is set as
foreign_sortby, the DataHandler will write these integers into that field, which is most likely not what you want. Use
foreign_default_sortbyin this case.
This property requires that the foreign_field approach is used.
When using MM relations the field used on the intermediate table is hardcoded to
sorting_foreign. Setting this property has no effect combined with an MM table.
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.