Functions in `write-region-annotate-functions' might make another buffer the current one instead of returning a list of annotations. This is a very useful behaviour, it could be mentioned in the docstring to make it official. I could provide a first draft of the new docstring if you want to make this behaviour official. Looking at (fileio.c)build_annotations shows that behavior of functions in `write-region-annotate-functions' is basically the same as the encode functions in format-alist. For the encode functions, it is mentioned that they could change the buffer contexts (see MODIFY in the docstring of `format-alist'). - Christoph P.S. in the alpha version of my package x-symbol, I use a function safely in `write-region-annotate-functions' (since March) where x-symbol-encode copies the contexts to the third arg, switches to that buffer and does changes there... (defun x-symbol-write-region-annotate-function (start end) (and x-symbol-mode x-symbol-token-language (let ((selective selective-display)) (when (x-symbol-encode x-symbol-safe-exec-threshold (null x-symbol-file-has-8bits) (get-buffer-create " x-symbol conversion ")) (setq selective-display selective) t)) (message "X-Symbol Conversion in write-region%s" ; only alpha version (if font-lock-mode " with font-lock" " (fast)"))) nil)