um-mode : restrict movement to bolp with cursor-intangible-mode

um.el

@@ -455,7 +455,15 @@ Optional TAGS string may contain more than one tag separated by a comma.
 
 \\{um-mode-map}
 "
-  (read-only-mode)
-  )
+  ;; restrict movement to (bolp) with cursor-intangible-mode
+  (save-excursion
+    (goto-char (point-min))
+    (while (not (eobp))
+      ;; NOTE: actually the newline is the only position not included, but this
+      ;; positions the cursor visually at the bol:
+      (put-text-property (pos-bol) (pos-eol) 'cursor-intangible t)
+      (forward-line 1)))
+  (cursor-intangible-mode)
+  (read-only-mode))
 
 (provide 'um)