Customization list

[Ergus]

Hi:

After some years in emacs I still have issues when creating
customization variables:

The examples in the documentation are very simple, but getting some
typical simple behaviors is a bit hard to get from them.

Suppose I have a variable:

(defcustom my-features '(feature1 feature2 feature3)
  :type ???)

This is a variable that may have a list of possible determined values,
so I was expecting to get something like this in the customization menu:

[x] feature1
[x] feature2
[x] feature3
[ ] feature4
[ ] feature5

So, when the user adds or removes one of the choices, the variable gets
a final value associated.

I was trying to use different combination of choice, radio, set, repeat
and const, but there were some issues with each.

Is this very simple "custom menu" approach possible?

Is so, please, could you share some example (either inlined here or a
variable name existent in vanilla) with such behavior.

Thanks in advance,
Ergus