Writing a custom treater for HTML articles

[Sean McAfee]

As I noted in an earlier article, choosing w3m for mm-text-html-renderer
takes a very long time on large messages, while w3m-standalone is much
faster, but produces plainer output.  I tried to write a function that
dispatches to one or the other based on the size of the message, but so
far without success.  Here was my effort:

(defun render-html-appropriately ()
  (if (< (buffer-size) 50000)
      (gnus-article-wash-html-with-w3m)
    (gnus-article-wash-html-with-w3m-standalone)))

When I viewed an HTML message, I got this error:

  mm-inline-text-html: Wrong number of arguments: (...), 1

So apparently an argument is expected, but I can't tell what it is;
mm-inline-text-html is not documented.  I rewrote my function:

(defun render-html-appropriately (&rest args)
  (insert (format "%s" args)))

Now this gets inserted into the message buffer:

  (( *mm*<3> (text/html) nil nil nil nil nil nil))

Not very helpful.

What's the right way to write a renderer?  The docs suggest to me that
the rendering function would simply be called without arguments in the
buffer to be treated, but apparently it's more complicated than that.