How to properly specify defcustom default list of non-trivial data types?

Question

How to properly write the default value for a non-trivial defcustom form in standard for something like I have below: a list of 3-element lists, with choices of the types?

The defcustom form is: defcustom option standard doc [keyword value]...

The following defcustom works fine as long as it's default is nil.

As soon as I add a non-empty list of values in standard for the default value, Emacs *Customize* buffer UI fails (see below).

#1: My defcustom form: (with a nil value for the default, Emacs *Customize* buffer UI works fine):

(defcustom pel-key-chords nil
"..."
:group 'pel-pkg-for-key-chord
  :type '(repeat
          (choice
           (list
            :tag "expansion-keys"
            (symbol       :tag "mode           " :value global)
            (string       :tag "the 2 keys     ")
            (repeat
             (key-sequence :tag "key")))
           (list
            :tag "command"
            (symbol       :tag "mode           " :value global)
            (string       :tag "the 2 keys     ")
            (function     :tag "command        "))
           (list
            :tag "lambda"
            (symbol       :tag "mode           " :value global)
            (string       :tag "the 2 keys     ")
            (function     :tag "elisp code     "
                          :value (lambda () (interactive) <YOUR CODE HERE>))))))

The problem occurs when I specify a list of elements, or just one for default, as shown below:

#2: My defcustom form: (same code, but with an explicit default of one element):

(defcustom pel-key-chords
'((global   "<>"  "<>\C-b"))
"..."
...

With the default, Emacs *Customize* buffer UI fails: the INS and DEL buttons are not available and it is impossible to add or delete elements.

I read Emacs Lisp Customization Settings section and some code like the dump-jump.el code that defines some complex data with initialization. I assume I must identify some keywords in my declaration of the default, but for some reason I can't find the proper syntax for initializing the data I defined above.

Answer 1

Well, murphy's law strikes again...

I just realized that the Customize buffer was showing mismatch beside the data structure...

The problem I had tied to the fact that the last element of my inner list is itself a list, and the default declaration identified just 1 string.

So instead of writing

(defcustom pel-key-chords 
'((global "<>" "<>\C-b"))
"..."
...

What I need to do is to write it like this:

(defcustom pel-key-chords 
'((global "<>" ("<>\C-b")))
"..."
...

and all goes well.

I wish checkdoc was able to catch these types of errors.