RE: Why is M-; not showing up in <lang-mode> C-h m help?

[Drew Adams <drew.adams@oracle.com>]

FWIW, with Icicles key completion (`S-TAB') you get the entire
set of current key bindings, organdized hierarchically by prefix
keys.  This includes the menu-bar menus.  (If you use library
`tool-bar+.el' then you even have access to the tool-bar "keys"
- aka buttons.)

All of the keys and their associated commands are visible as
completion candidates in *Completions*.

And all of their doc strings are available by cycling using
`C-M-down' or by clicking `C-mouse2' on candidates in
*Completions*.

If you know the key prefix you want, you can hit that first
and then use `S-TAB' to see the keys with that prefix, etc.

Your minibuffer input filters the set of candidates, of course.
You can filter by key name or command name or both.  You can
browse & cycle among the matching candidates.

You can use multiple patterns (separated by `S-SPC') for this
filtering (progressive completion).

A lot better than `C-h b'.  And it's not just for help.
Choosing a complete candidate invokes its command.

http://www.emacswiki.org/emacs/Icicles_-_Key_Completion

`C-h k S-TAB' tells you this:

,----
| Complete a key sequence for the currently invoked prefix key.
| Input-candidate completion and cycling are available.
| 
| By default, key completion is case insensitive.  As always, you can
| use `C-A' to toggle case sensitivity.
| 
| You can navigate the key-binding hierarchy (prefix-key hierarchy),
| just as would navigate a file-system hierarchy (to complete directory
| and file names) or a menu hierarchy (to complete submenu and menu-item
| names).
| 
| Completion candidates generally have the form `KEY  =  COMMAND'.
| 
| If COMMAND is `...', then KEY is a prefix key; choosing it updates the
| completion candidates list to the keys under that prefix.  For
| example, choosing `C-x = ...' changes the candidates to those with
| prefix `C-x'.
| 
| The special candidate `..' means to go up one level of the key-binding
| hierarchy and complete candidates there.  For example, if you are
| currently completing prefix key `C-x 5', and you choose candidate
| `..', then you will be completing prefix `C-x', the parent of `C-x 5'.
| 
| Except at the top level, the default value for completion is `..'.
| 
| You can use `C-M-,' at any time to switch between sorting with local
| bindings first and sorting with prefix keys first.  You can use `C-,'
| at any time to change the sort order among these two and sorting by
| command name.
|
...
| While cycling, these keys describe candidates:
| 
| `C-RET'   - Describe command of current completion candidate only
| `C-down'  - Move to next completion candidate and describe
| `C-up'    - Move to previous completion candidate and describe
...
| `C-!'     - Describe *all* candidates (or all that are saved),
|             successively - use the [back] button in buffer *Help* to
|             visit the descriptions
...
| With prefix `C-M-' instead of `C-', the same keys (`C-M-mouse-2',
| `C-M-down', and so on) provide help about candidates.
| 
| Use `mouse-2', `RET', or `S-RET' to finally choose a candidate, or
| `C-g' to quit.  This is an Icicles command - see command
| `icicle-mode'.
`----