TAB folds a frame, which is what the header always said it did

emacs/MANUAL.md

@@ -362,7 +362,7 @@ answers; anything that needs to know what a form means asks.
 longer empty. It lists the stopped program's frames, innermost first, each with
 where it is and how many named slots it has.
 
-`TAB` on a frame opens it and shows what its locals hold — name, type and
+`TAB` on a frame opens it (or `f`, which folds from anywhere on the frame) and shows what its locals hold — name, type and
 value, rendered the same way the inspector renders anything else. They are
 fetched the first time a frame is opened and then kept, because a stopped
 program's locals cannot change underneath you and a round trip behind a key

emacs/flan-cnr.el

@@ -383,11 +383,23 @@ list already says it."
       (get-text-property pos 'flan-cnr-frame)
       (get-text-property pos 'flan-cnr-inspect)))
 
+(defun flan-cnr-tab ()
+  "Fold this frame, or move to the next actionable line.
+
+TAB does two things because the buffer has two kinds of line and the section
+header already promised the first one: on a frame, it opens or closes that
+frame's locals; anywhere else, it moves. `f' still folds unconditionally, for
+anyone who would rather TAB always moved."
+  (interactive)
+  (if (get-text-property (point) 'flan-cnr-frame)
+      (flan-cnr-toggle-frame)
+    (flan-cnr-next)))
+
 (defvar flan-cnr-mode-map
   (let ((map (make-sparse-keymap)))
     (define-key map (kbd "RET") #'flan-cnr-take)
     (define-key map [mouse-1] #'flan-cnr-take)
-    (define-key map (kbd "TAB") #'flan-cnr-next)
+    (define-key map (kbd "TAB") #'flan-cnr-tab)
     (define-key map [backtab] #'flan-cnr-previous)
     (define-key map "n" #'flan-cnr-next)
     (define-key map "p" #'flan-cnr-previous)