26675: add POSIX_ALIASES option

Doc/Zsh/options.yo

@@ -1708,6 +1708,43 @@ is not and will replace the first element of the array.
 This option is for compatibility with older versions of the shell and
 is not recommended in new code.
 )
+pindex(POSIX_ALIASES)
+pindex(NO_POSIX_ALIASES)
+pindex(POSIXALIASES)
+pindex(NOPOSIXALIASES)
+item(tt(POSIX_ALIASES) <K> <S>)(
+When this option is set, reserved words are not candidates for
+alias expansion:  it is still possible to declare any of them as an alias,
+but the alias will never be expanded.  Reserved words are
+tt(!),
+tt([[),
+tt({),
+tt(}),
+tt(case),
+tt(coproc),
+tt(do),
+tt(done),
+tt(elif),
+tt(else),
+tt(end),
+tt(esac),
+tt(fi),
+tt(for),
+tt(foreach),
+tt(function),
+tt(if),
+tt(nocorrect),
+tt(repeat),
+tt(select),
+tt(then),
+tt(time),
+tt(until),
+tt(while).
+
+Alias expansion takes place while text is being read; hence when this
+option is set it does not take effect until the end of any function or
+other piece of shell code evaluated as one unit.
+)
 pindex(POSIX_BUILTINS)
 pindex(NO_POSIX_BUILTINS)
 pindex(POSIXBUILTINS)