12.2.3  Scripts in <code class="filename">/etc/grub.d</code>

https://doc.opensuse.org/documentation/leap/reference/html/book.opensuse.reference/cha.grub2.html#sec.grub2.etc_grub_d

Information about 40_custom and 90_persistent are not fully clear.

1) How are 40_custom and 90_persistent related to each other?  Why does one
prefer over the other?  40_custom seems more flexible than 90_persistent.

2) In case of 90_persistent information seems to be missing.  The lines to be
stored in the /boot/grub2/grub.cfg must be between the lines:

### BEGIN /etc/grub.d/90_persistent ###
<data to be put here>
### END /etc/grub.d/90_persistent ###

It would be good to mention this requirement here.

However, in the beginning of grub.cfg the following warning is stated:
# head /boot/grub2/grub.cfg
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub2-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub

As such, I would be good to mention that for 90_persistent this warning must be
neglected.

Perhaps in more general (refer to my remark 1) above ), it's probably better,
easier to use 40_custom instead of 90_persistent.  Is there a good reason for
90_persistent?  If so, have it mentioned in the 90_persistent explanation
please.