manual: Add an example using :setup-children

docs/transient.org

@@ -1012,7 +1012,10 @@ constructor of that class.
   to use the same form as understood by ~transient-define-prefix~,
   described below.  If you use the latter approach, you can use the
   ~transient-parse-suffixes~ and ~transient-parse-suffix~ functions to
-  transform them from the convenient to the expected form.
+  transform them from the convenient to the expected form.  Depending
+  on the used group class, ~transient-parse-suffixes~'s SUFFIXES must be
+  a list of group vectors (for ~transient-columns~) or a list of suffix
+  lists (for all other group classes).
 
   If you explicitly specify children and then transform them using
   ~:setup-children~, then the class of the group is determined as usual,
@@ -1024,6 +1027,32 @@ constructor of that class.
   is used and a warning is displayed.  This warning will eventually
   be replaced with an error.
 
+  #+BEGIN_SRC emacs-lisp
+    (transient-define-prefix my-finder-by-keyword ()
+      "Select a keyword and list matching packages."
+      ;; The real `finder-by-keyword' is more convenient
+      ;; of course, but that is not the point here.
+      [:class transient-columns
+       :setup-children
+       (lambda (_)
+         (transient-parse-suffixes
+          'my-finder-by-keyword
+          (let ((char (1- ?A)))
+            (mapcar                  ; a list ...
+             (lambda (partition)
+               (vconcat              ; of group vectors ...
+                (mapcar (lambda (elt)
+                          (let ((keyword (symbol-name (car elt))))
+                                     ; ... where each suffix is a list
+                            (list (format "%c" (cl-incf char))
+                                  keyword
+                                  (lambda ()
+                                    (interactive)
+                                    (finder-list-matches keyword)))))
+                        partition)))
+             (seq-partition finder-known-keywords 7)))))])
+  #+END_SRC
+
 - The boolean ~:pad-keys~ argument controls whether keys of all suffixes
   contained in a group are right padded, effectively aligning the
   descriptions.

docs/transient.texi

@@ -1201,7 +1201,10 @@ prefix's @code{transient--layout} property, but it is often more convenient
 to use the same form as understood by @code{transient-define-prefix},
 described below.  If you use the latter approach, you can use the
 @code{transient-parse-suffixes} and @code{transient-parse-suffix} functions to
-transform them from the convenient to the expected form.
+transform them from the convenient to the expected form.  Depending
+on the used group class, @code{transient-parse-suffixes}'s SUFFIXES must be
+a list of group vectors (for @code{transient-columns}) or a list of suffix
+lists (for all other group classes).
 
 If you explicitly specify children and then transform them using
 @code{:setup-children}, then the class of the group is determined as usual,
@@ -1213,6 +1216,32 @@ For backward compatibility, if you fail to do so, @code{transient-column}
 is used and a warning is displayed.  This warning will eventually
 be replaced with an error.
 
+@lisp
+(transient-define-prefix my-finder-by-keyword ()
+  "Select a keyword and list matching packages."
+  ;; The real `finder-by-keyword' is more convenient
+  ;; of course, but that is not the point here.
+  [:class transient-columns
+   :setup-children
+   (lambda (_)
+     (transient-parse-suffixes
+      'my-finder-by-keyword
+      (let ((char (1- ?A)))
+        (mapcar                  ; a list ...
+         (lambda (partition)
+           (vconcat              ; of group vectors ...
+            (mapcar (lambda (elt)
+                      (let ((keyword (symbol-name (car elt))))
+                                 ; ... where each suffix is a list
+                        (list (format "%c" (cl-incf char))
+                              keyword
+                              (lambda ()
+                                (interactive)
+                                (finder-list-matches keyword)))))
+                    partition)))
+         (seq-partition finder-known-keywords 7)))))])
+@end lisp
+
 @item
 The boolean @code{:pad-keys} argument controls whether keys of all suffixes
 contained in a group are right padded, effectively aligning the