>
> >  (defun svg--append (svg node)
> > +  ;; id is expected to be unique.
> >    (let ((old (and (dom-attr node 'id)
> >                 (dom-by-id svg
> >                               (concat "\\`" (regexp-quote (dom-attr node
> 'id))
> >                                       "\\'")))))
> >      (if old
> > -        ;; FIXME: This was (dom-set-attributes old (dom-attributes
> node))
> > -        ;; and got changed by commit
> f7ea7aa11f6211b5142bbcfc41c580d75485ca56
> > -        ;; without any explanation.
> > -     (setcdr (car old) (cdr node))
> > -      (dom-append-child svg node)))
> > +        ;; Remove old node. New node might be a different type.
> > +        (mapc (lambda (a)
> > +                  (dom-remove-node svg a))
> > +                old))
> > +    (dom-append-child svg node))
>
> Hm...  I think this is basically correct, but it's a behaviour change --
> previously svg--append wouldn't append if the ID already existed, but
> would keep the save place in the structure, but with this change, it
> really always appends.
>
> So I don't think that's quite right -- the old behaviour was OK, I think
> (but undocumented).
>
Existing code doesn't ensure ids are unique. Furthermore, in case id is
duplicated, only the attributes on the first tag gets replaced. That's a
little unpredictable behaviour from an API perspective.