52510: document how ${ ... } et al. affect use of "private"; add index entries

ChangeLog

@@ -1,5 +1,8 @@
 2024-01-28  Bart Schaefer  <schaefer@zsh.org>
 
+	* 52510: Doc/Zsh/expn.yo, Doc/Zsh/mod_private.yo: document how
+	${ ... } et al. affect use of "private"; add index entries
+
 	* 52509: configure.ac, Src/utils.c: manage internals of stdio
 	objects when performing redirections.
 

Doc/Zsh/expn.yo

@@ -1915,6 +1915,9 @@ from the final replacement in this case, and it is subject to filename
 generation in the same way as `tt($LPAR())...tt(RPAR())' but is em(not)
 split on tt(IFS) unless the tt(SH_WORD_SPLIT) option is set.
 
+cindex(substitution, command, current shell)
+cindex(substitution, command, non forking)
+cindex(substitution, nofork)
 Substitutions of the form `tt(${|)var(param)tt(|)...tt(})' are similar,
 except that the substitution is replaced by the value of the parameter
 named by var(param).  No implicit save or restore applies to var(param)

Doc/Zsh/mod_private.yo

@@ -84,6 +84,9 @@ created outside the local scope when it was not previously declared.)
 itemiz(An exported private remains in the environment of inner scopes but
 appears unset for the current shell in those scopes.  Generally, exporting
 private parameters should be avoided.)
+itemiz(Declaring a private parameter in a current shell command substitution
+such as `tt(${ )...tt( })' limits the parameter to the scope of the command
+substitution, just as if the parameter were declared in a function.)
 enditemize()
 
 Note that this differs from the static scope defined by compiled languages