partman primary vs secondary partitions

[Andre Rodier <andre@rodier.me>]

Hello,

I am testing the Debian Stretch preseed, and I have a question about the 
partition scheme.

I am using the following block in my partition recipe, and it works so 
far:

d-i partman-auto-raid/recipe string		\
	1 2 0 ext3 /boot			\
	/dev/sda1#/dev/sdb1			\
	.					\
	1 2 0 lvm -				\
	/dev/sda5#/dev/sdb5 			\
	.					\

My question is, "how can I create two primary partitions instead of an 
extended partition ?" and of course, is this possible ?

I am also happy to use GPT partitioning scheme.

Thanks,
André