Further, I can't seem to get these functions to work /as documented/ or 
expected.

Without these defined when I'm creating a widget with the following 
code, I do get a button but the internal value is displayed in the 
clickable button. I'd like the external value to be displayed in the 
button %v, just as the menu-tag is is "externally facing".

<<widget>>=
(define-widget 'project-widget 'list
   :tag (let ((s "\n\tProject"))
          (put-text-property 0 (length s) 'face 'bold s) s)
   :format "%t\n%v "
   :offset 0
   :indent 0
   :convert-widget 'widget-types-convert-widget
   :args '((menu-choice
            :tag "EmacSQL-supported backend"
            :format "%[%t%]: %[%v%]"
            :value "sqlite"
            :value-to-external <<menu-choice internal value to external lambda>>
            :value-to-internal <<menu-choice external value to internal lambda>>
            (choice-item :menu-tag "MySQL" :value "mysql")
            (choice-item :menu-tag "PostgreSQL" :value "postgresql")
            (choice-item :menu-tag "SQLite" :value "sqlite"))))
<<menu-choice internal value to external lambda>>=
(lambda (widget internal-value)
   "Converts lowercase, internal values to the casing of trademarks."
   (pcase internal-value
     ("mysql" "MySQL")
     ("sqlite" "SQLite")
     ("postgresql" "PostgreSQL")))
<<menu-choice external value to internal lambda>>=
(lambda (widget external-value)
   "Converts the casing of trademarked names to lowercase, internal values."
   (pcase external-value
     ("MySQL" "mysql")
     ("SQLite" "sqlite")

On 7/14/23 00:32, Bryce Carson wrote:
>
> In the section /Defining New Widgets/, the following quotation reveals 
> a bug, I believe. I added emphasis for the last sentence of each 
> description of the keywords. I believe that for the :value-to-external 
> function, the last sentence is not supposed to be present.
>
> :value-to-internal
> 	Function to convert the value to the internal format. The function takes two
> 	arguments, a widget and an external value, and returns the internal value./The function is called on the present :value when the widget is 
> created, and on any value set later with widget-value-set./
> :value-to-external
> 	Function to convert the value to the external format. The function takes two
> 	arguments, a widget and an internal value, and returns the external value./The function is called on the present :value when the widget is 
> created, and on any value set later with widget-value-set./
>
> It looks like the author or editor of the descriptions coped them, 
> which is fine. It doesn't make sense that :value-to-external would be 
> called when the widget is created, nor when new values are set with 
> widget-value-set.
>
> Other places in the manual state that the value of the :value keyword, 
> when creating or defining widget, should be in the external form, more 
> evidence that the last sentence is a bug.
>
-- 
"It's a GNU system, I don't know this!"
||--- Mirror universe Lex Murphy, in Cenozoic Zoo