document export x=1 y=$x

[jidanni]

On the man page at section "export", mention that the latter below
will not do what one expects, as here revealed:
$ set -x
$ a=1 b=$a
+ a=1
+ b=1
$ export x=1 y=$x
+ export x=1 y=
+ x=1
+ y=
Yes I'm sure it is mentioned elsewhere on the page but you might want
to drum it home again here. Maybe also at $ help export.