(completion-at-point-functions): Improve doc

(cherry picked from commit b56c56f203f8b066dd71e6ae6a254121b3ac3f08)

1 files changed, 6 insertions, 1 deletions

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 7302fff4584..ced0ce64b50 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -2076,7 +2076,12 @@ Currently supported properties are all the properties that can appear in
    match the text at point, then instead of reporting a completion
    failure, the completion should try the next completion function.
 As is the case with most hooks, the functions are responsible for
-preserving things like point and current buffer.")
+preserving things like point and current buffer.
+
+NOTE: These functions should be cheap to run since they're sometimes run from
+`post-command-hook' and they should ideally only choose which kind of
+completion table to use and not pre-filter it based on the current text between
+START and END (e.g. that would not obey `completion-styles').")
 
 (defvar completion--capf-misbehave-funs nil
   "List of functions found on `completion-at-point-functions' that misbehave.