manual: move pattern open out of the extension chapter (#8950)

* move the grammar description to the pattern section of the language reference
* add a small example in the module chapter of the tutorial

Changes

@@ -156,6 +156,12 @@ Working version
 - #1939, #2023: Implement Unix.truncate and Unix.ftruncate on Windows.
   (Florent Monnier and Nicolás Ojeda Bär, review by David Allsopp)
 
+### Manual and documentation:
+
+- #8950: manual, move local opens in pattern out of the extension chapter
+  (Florian Angeletti, review and suggestion by Gabriel Scherer)
+
+
 ### Compiler user-interface and warnings:
 
 - #8833: Hint for (type) redefinitions in toplevel session

manual/manual/refman/exten.etex

@@ -330,34 +330,6 @@ constructors of [t] could be present.
 Similarly to abstract types, the variance of type parameters
 is not inferred, and must be given explicitly.
 
-
-\section{Local opens for patterns}
-\ikwd{let\@\texttt{let}}
-\ikwd{open\@\texttt{open}} \label{s:local-opens}
-
-(Introduced in OCaml 4.04)
-
-\begin{syntax}
-pattern:
-       ...
-     | module-path '.(' pattern ')'
-     | module-path '.[' pattern ']'
-     | module-path '.[|' pattern '|]'
-     | module-path '.{' pattern '}'
-
-\end{syntax}
-
-For patterns, local opens are limited to the
-@module-path'.('pattern')'@ construction. This
-construction locally open the module referred to by the module path
-@module-path@ in the scope of the pattern @pattern@.
-
-When the body of a local open pattern is delimited by
-@'[' ']'@,  @'[|' '|]'@,  or @'{' '}'@, the parentheses can be omitted.
-For example, @module-path'.['pattern']'@ is equivalent to
-@module-path'.(['pattern'])'@, and @module-path'.[|' pattern '|]'@ is
-equivalent to @module-path'.([|' pattern '|])'@.
-
 \section{Locally abstract types}
 \ikwd{type\@\texttt{type}}
 \ikwd{fun\@\texttt{fun}} \label{s:locally-abstract}

manual/manual/refman/patterns.etex

@@ -22,9 +22,12 @@ pattern:
   | char-literal '..' char-literal
   | 'lazy' pattern
   | 'exception' pattern
+  | module-path '.(' pattern ')'
+  | module-path '.[' pattern ']'
+  | module-path '.[|' pattern '|]'
+  | module-path '.{' pattern '}'
 \end{syntax}
 See also the following language extensions:
-\hyperref[s:local-opens]{local opens},
 \hyperref[s-first-class-modules]{first-class modules},
 \hyperref[s:attributes]{attributes} and
 \hyperref[s:extension-nodes]{extension nodes}.
@@ -225,3 +228,18 @@ call.
 A pattern match must contain at least one value case. It is an error if
 all cases are exceptions, because there would be no code to handle
 the return of a value.
+
+\subsubsection*{Local opens for patterns}
+\ikwd{open\@\texttt{open}} \label{s:local-opens-pattern}
+(Introduced in OCaml 4.04)
+
+For patterns, local opens are limited to the
+@module-path'.('pattern')'@ construction. This
+construction locally opens the module referred to by the module path
+@module-path@ in the scope of the pattern @pattern@.
+
+When the body of a local open pattern is delimited by
+@'[' ']'@,  @'[|' '|]'@,  or @'{' '}'@, the parentheses can be omitted.
+For example, @module-path'.['pattern']'@ is equivalent to
+@module-path'.(['pattern'])'@, and @module-path'.[|' pattern '|]'@ is
+equivalent to @module-path'.([|' pattern '|])'@.

manual/manual/tutorials/moduleexamples.etex

@@ -99,6 +99,12 @@ becomes
 \begin{caml_example}{toplevel}
   PrioQueue.[insert empty 1 "hello"];;
 \end{caml_example}
+This second form also works for patterns:
+\begin{caml_example}{toplevel}
+  let at_most_one_element x = match x with
+  | PrioQueue.( Empty| Node (_,_, Empty,Empty) ) -> true
+  | _ -> false ;;
+\end{caml_example}
 
 It is also possible to copy the components of a module inside
 another module by using an "include" statement. This can be