functions

This is what the partman d-i module does:

interact with the user on a different way then using debconf
"partitioning"
- create partitions
- delete partitions
- resize partitions
create filesystems in the partitions
create the file /etc/fstab (the definition of the mount positions of the filesystems)

Undocumented options

The following options are not fully explained in the official documentation:

method{ biosgrub }: Configure this to be a BIOS boot partition, so GRUB can boot a GPT disk on a machine without UEFI support.
$iflabel{ }: Exclude partitions that are only for a different disk label. Support for multiple space-separated disk labels was added in MR #22 (available in trixie).
$reusemethod{ }: Check if we can reuse an existing partition. The original commit says it's "to help us reuse existing EFI system partitions".
$bios_boot{ }: bug #491376 (from 2009) suggests this was replaced by method{ biosgrub }.
$gptonly{ }: Usage examples (e.g. this one from 2021) suggest this was a synonym for $iflabel{ gpt }