In zsh-workers 27648 and 27650 (commit 8ac97f33, back in 2010), the
"repeat" reserved word was disabled when zsh starts in any emulation
mode, to avoid interfering with sh scripts when zsh is invoked as sh.

(Note that this change disabled the (t)csh-style 'repeat' loop even if
zsh is invoked as csh. It seems unlikely that was intended.)

Meanwhile, I've identified five other reserved words that are unique to
zsh *and* are perfectly plausible function names, so could kill an sh or
ksh/bash script:

	end
	float
	foreach
	integer
	nocorrect

So I think they (and 'repeat') should be disabled if zsh is invoked in
sh or ksh emulation mode.

'float' and 'integer' are part of the typeset family, so the underlying
builtins would be exposed. It would then be inconsistent not to do the
same with the rest of the typeset family:

	declare
	export
	local
	readonly
	typeset

Thankfully, the KSH_TYPESET option still works. It should revert to
being automatically enabled for ksh emulation and not for sh emulation,
as in zsh up to 5.0.8.

Treating the whole typeset family as builtins subject to KSH_TYPESET
actually increases the accuracy of sh and ksh emulation modes.

One issue is that POSIX explicitly specifies 'export' and 'readonly' as
special builtins and not as reserved words. So POSIX scripts should be
able to override them at least with an alias.[*] This breaks if they are
reserved words.

For the incomplete csh emulation mode (does anyone actually use this?)
it's probably not worth bothering to disable anything, so instead of
testing for !EMULATION(EMULATE_ZSH) we should test for
EMULATION(EMULATE_SH) || EMULATION(EMULATE_KSH). This restores 'repeat'
when zsh is invoked as csh.

By the way, contrary to claims in the documentation, the KSH_TYPESET
option was never completely obsolete. Even with the post-5.0.8 reserved
word interface activated, the behaviour of MAGIC_EQUAL_SUBST still takes
KSH_TYPESET into account.

Thanks,

- Martijn

[*] This is useful if a sh script needs to parse the output of 'export
-p' (or 'readonly -p'). It is not possible to grep their output reliably
as entries may contain newlines. The only reliable POSIX way is to have
the shell parse it, which is done by temporarily aliasing 'export' to a
handler shell function and doing an 'eval "$(export -p)"'.