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diff --git a/sbin/bectl/bectl.8 b/sbin/bectl/bectl.8
--- a/sbin/bectl/bectl.8
+++ b/sbin/bectl/bectl.8
@@ -17,7 +17,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd January 6, 2021
+.Dd March 31, 2022
.Dt BECTL 8
.Os
.Sh NAME
@@ -131,6 +131,9 @@
If the
.Fl r
flag is given, a recursive boot environment will be made.
+See
+.Sx Boot Environment Structures
+for a discussion on different layouts.
.Pp
If the
.Fl e
@@ -155,6 +158,9 @@
.Fl r
flag is given, a recursive snapshot of the boot environment will be created.
A snapshot is created for each descendant dataset of the boot environment.
+See
+.Sx Boot Environment Structures
+for a discussion on different layouts.
.Pp
No new boot environment is created with this command.
.It Xo
@@ -345,6 +351,90 @@
or
.Fl \&?
is specified.
+.Ss Boot Environment Structures
+The traditional
+.Fx
+boot environment layout, as created by the Auto ZFS option to
+.Xr bsdinstall 8 ,
+is a
+.Dq shallow
+boot environment structure, where boot environment datasets do not have any
+directly subordinate datasets.
+Instead, they're organized off in
+.Pa zroot/ROOT ,
+and they rely on datasets elsewhere in the pool having
+.Dv canmount
+set to
+.Dv off .
+For instance, a simplified pool may be laid out as such:
+.Bd -literal -offset indent
+% zfs list -o name,canmount,mountpoint
+NAME CANMOUNT MOUNTPOINT
+zroot
+zroot/ROOT noauto none
+zroot/ROOT/default noauto none
+zroot/usr off /usr
+zroot/usr/home on /usr/home
+zroot/var on /var
+.Ed
+.Pp
+In that example,
+.Pa zroot/usr
+has
+.Dv canmount
+set to
+.Dv off ,
+thus files in
+.Pa /usr
+typically fall into the boot environment because this dataset is not mounted.
+.Pa zroot/usr/home
+is mounted, thus files in
+.Pa /usr/home
+are not in the boot environment.
+.Pp
+The other style of boot environments in use, frequently called
+.Dq deep boot environments ,
+organizes some or all of the boot environment as subordinate to the boot
+environment dataset.
+For example:
+.Bd -literal -offset indent
+% zfs list -o name,canmount,mountpoint
+NAME CANMOUNT MOUNTPOINT
+zroot
+zroot/ROOT noauto none
+zroot/ROOT/default noauto none
+zroot/ROOT/default/usr noauto /usr
+zroot/ROOT/default/usr/local noauto /usr/local
+zroot/var on /var
+.Ed
+.Pp
+Note that the subordinate datasets now have
+.Dv canmount
+set to
+.Dv noauto .
+These are more obviously a part of the boot environment, as indicated by their
+positioning in the layout.
+These subordinate datasets will be mounted by the
+.Dv zfsbe
+.Xr rc 8
+script at boot time.
+In this example,
+.Pa /var
+is excluded from the boot environment.
+.Pp
+.Nm
+commands that have their own
+.Fl r
+operate on this second,
+.Dq deep
+style of boot environment, when the
+.Fl r
+flag is set.
+A future version of
+.Nm
+may default to handling both styles and deprecate the various
+.Fl r
+flags.
\" .Sh EXAMPLES
\" .Bl -bullet
\" .It

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