heredoc and subshell

[Oleg Bulatov <oleg@bulatov.me>]

Hello,

trying to minimize a shell code I found an unobvious moment with heredocs and subshells.

Is it specified by POSIX how next code should be parsed? dash output for this code differs from bash and zsh.

--- code
prefix() { sed -e "s/^/$1:/"; }
DASH_CODE() { :; }

prefix A <<XXX && echo "$(prefix B <<XXX
echo line 1
XXX
echo line 2)" && prefix DASH_CODE <<DASH_CODE
echo line 3
XXX
echo line 4)"
echo line 5
DASH_CODE

--- bash 4.3.42 output:
A:echo line 3
B:echo line 1
line 2
DASH_CODE:echo line 4)"
DASH_CODE:echo line 5

--- dash 0.5.8 output:
A:echo line 1
B:echo line 2)" && prefix DASH_CODE <<DASH_CODE
B:echo line 3
line 4
line 5

-- 
Oleg