RE: (debug) backtrace: how to show source code at current location.

[Drew Adams]

> > C-h i m Elisp i define-key
> 
> Thanks Drew.
> Doing that got me to an info page with:
> 
>      If KEY is `[t]', this sets the default binding in 
> KEYMAP.  When an
>      event has no binding of its own, the Emacs command loop uses the
>      keymap's default binding, if there is one.
> 
> but that doesn't tell me what are the possible values for t in `[t]'.
> How did you know that "iso-left-tab" was a possible value for t?
> As mentioned in my other post, I found grep.el had "backtab" instead
> of "iso-left-tab".  I tried fishing through several info files after
> the define-key one; however, none I viewed showed what the possible
> values were for the t in [t].

No, [t] is something else, which you needn't worry about here.

> Where is this information?

On the same page I indicated (`i define-key' -> node `Changing Key Bindings').
It says:

 In writing the key sequence to rebind, it is good to use the special
 escape sequences for control and meta characters (*note String Type::).
 The syntax `\C-' means that the following character is a control
 character and `\M-' means that the following character is a meta
 character.  Thus, the string `"\M-x"' is read as containing a single
 `M-x', `"\C-f"' is read as containing a single `C-f', and `"\M-\C-x"'
 and `"\C-\M-x"' are both read as containing a single `C-M-x'.  You can
 also use this escape syntax in vectors, as well as others that aren't
 allowed in strings; one example is `[?\C-\H-x home]'.  *Note Character
 Type::.

Notice the last sentence, before the Note.  The example uses the `home' function
key, but a simpler example such as [iso-left-tab] would be easier to understand
for just a function key alone.

The paragraph that follows that one also discusses key notation.

Also, `i function keys' takes you to node `Function Keys', which describes keys
such as `iso-left-tab' (aka `<iso-left-tab>'.

Node `Menu Example' also mentions the vector notation for function keys (such as
[iso-left-tab]).

I agree that there doesn't seem to be an example in node `Changing Key Bindings'
of the vector notation with a simple function key.  And it would help for that
node to have some cross references to the other nodes.  And it's possible that a
complete discussion of this is elsewhere in the manual somewhere.  Why not file
a doc bug to have this info made more noticeable and easier to find?  To do
that: `M-x report-emacs-bug'.  Thx.