[PATCH] Document imperfections in POSIX/sh compatibility

[dana <dana@xxxxxxx>]

Lawrence bumping 47794 reminded me of this. Someone on IRC was trying to use
zsh as sh and they were very annoyed to learn that the sh emulation has
imperfections that aren't really documented anywhere. I said i would add a
mention. Let me know if this is editorialising it too much

dana


diff --git a/Doc/Zsh/compat.yo b/Doc/Zsh/compat.yo
index f1be15fee..a09187918 100644
--- a/Doc/Zsh/compat.yo
+++ b/Doc/Zsh/compat.yo
@@ -74,3 +74,8 @@ tt(PROMPT_SUBST)
 and
 tt(SINGLE_LINE_ZLE)
 options are set if zsh is invoked as tt(ksh).
+
+Please note that zsh's emulation of other shells, as well as the degree
+of its POSIX compliance, is provided on a `best effort' basis.  Full
+compatibility is not guaranteed, and is not necessarily a goal of the
+project.