nnimap-split-download-body removed?

[Bodertz <bodertz@gmail.com>]

Apologies for any issues posting this message.  This may be a duplicate.

I wrote a function which can do something useful with the body of a
message.  If worse comes to worse, I can run this function manually, but
my plan was to use splitting to automate this.

As documented in "(gnus)Fancy Mail Splitting", this can be done by
setting 'nnimap-split-download-body' to 't'.  See the last sentence:

  (: FUNCTION ARG1 ARG2 ...)’
      If the split is a list, and the first element is ‘:’, then the
      second element will be called as a function with ARGS given as
      arguments.  The function should return a SPLIT.
  
      For instance, the following function could be used to split based
      on the body of the messages:
  
           (defun split-on-body ()
             (save-excursion
               (save-restriction
                 (widen)
                 (goto-char (point-min))
                 (when (re-search-forward "Some.*string" nil t)
                   "string.group"))))
  
      The buffer is narrowed to the header of the message in question
      when FUNCTION is run.  That’s why ‘(widen)’ needs to be called
      after ‘save-excursion’ and ‘save-restriction’ in the example above.
      Also note that with the nnimap backend, message bodies will not be
      downloaded by default.  You need to set
      ‘nnimap-split-download-body’ to ‘t’ to do that (*note Client-Side
      IMAP Splitting).

However, this did not seem to work, although I haven't tested
thouroughly.  Looking through the git history of Emacs, it seems that
'nnimap-split-download-body' was removed a little over ten years ago.
An internal variable, 'nnimap-split-download-body-default' is still
present, but is as far as I can tell unused.

Have I missed something obvious?  Is there a new way to do this?  Am I
just out of luck?

Thanks.