reference: clarify significance of order for submodules

Merge to v6.1
(cherry picked from commit e044e4360b)

pkgs/racket-pkgs/racket-doc/scribblings/reference/eval-model.scrbl

@@ -822,6 +822,11 @@ imports from its enclosing module or vice-versa, then @tech{visits} or
 @tech{instantiations} of the two modules are independent, and thier
 implementations may even be loaded from bytecode at different times.
 
+A submodule declared with @racket[module] can import any preceding
+submodule declared with @racket[module]. A submodule declared with
+@racket[module*] can import any preceding module declared with
+@racket[module*] and any submodule declared with @racket[module].
+
 When a submodule declaration has the form @racket[(module* _name #f
 ....)], then all of the bindings of the enclosing module's bodies are
 visible in the submodule's body, and the submodule implicitly imports

pkgs/racket-pkgs/racket-doc/scribblings/reference/syntax.scrbl

@@ -332,7 +332,14 @@ Each addition for @racket[id] is combined in order to form the entire
 submodule using @racket[(module* id #f ....)] at the end of the
 enclosing module. If there is only one @racket[module+] for a given
 @racket[id], then @racket[(module+ id form ...)] is equivalent to
-@racket[(module* id #f form ...)].
+@racket[(module* id #f form ...)], but still moved to the end of the
+enclosing module.
+
+When a module contains multiple submodules declared with
+@racket[module+], then the relative order of the initial
+@racket[module+] declarations for each submodule determines the
+relative order of the @racket[module*] declarations at the end of the
+enclosing module.
 
 A submodule must not be defined using @racket[module+] @emph{and}
 @racket[module] or @racket[module*]. That is, if a submodule is made