I am trying to define a composite type using the "group" compositor (see Elisp Manual, section "Composite Types"). Previously, I managed to define a composite type with the "list" constructor.
The Elisp manual tells that these constructors ("group" and "list") are similar. I get a weird result in the "Customize interface" and an error message displayed in the echo area.
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(defcustom group '(1 2 3) "here, give a description of the user option." :type '(group integer integer integer))
I noticed the message "custom-variable-value-create: Bad format" in the "Messages" buffer.
The manual should be clarified. Someone had the same issue one decade ago: "No doc for `group' in custom :type".