Extended Partition Table
Partition table / Window / Extended Partition
You may edit the extended partition table the same way as the partition table.
If you would like to boot from a secondary partition, you have to activate that secondary partition within the extended partition table; then switch this extended partition from inactive to "active" in the bootprofile.
Some operating systems do not support booting from secondary partitions at all or only if no primary partition is visible.
The functionality of the bootmanager, unfortunately, is not available to secondary partitions. The entire extended partition can be either only completely visible or completely invisible. The selection of the active partition cannot be set in the bootprofile either.