mh-search-mode-help-messages

mh-search-mode-help-messages is a variable defined in `mh-search.el'.
Its value is

((nil "Perform search:   \\[mh-index-do-search]\n" "Search with pick: \\[mh-pick-do-search]\n\n" "Move to a field by typing C-c C-f C-\n" "where  is the first letter of the desired field\n" "(except for From: which uses \"m\")."))

Documentation:
Key binding cheat sheet.

This is an associative array which is used to show the most common
commands. The key is a prefix char. The value is one or more strings
which are concatenated together and displayed in the minibuffer if ?
is pressed after the prefix character. The special key nil is used to
display the non-prefixed commands.

The substitutions described in `substitute-command-keys' are performed
as well.