Probably against best practices to commit monolithic patches, but this
is still an unreleased library, so I don't care.

Not really sure I care for the sexp-based regexps, but they do make it
easy to use the same regexp bits across several places, and I don't
have a lexer/parser handy, so they'll have to do for now.

For future reference, I used the following code to do this automatically, plus a
few minor manual edits (e.g., swapping rcurry and curry):

(defun seek-forward (term)
(let ((p (search-forward term nil t)))
(when p
(goto-char p))))

(defun swap-args ()
(interactive)
(save-excursion
(while (seek-forward "defmethod subject-p (")
(forward-sexp)
(transpose-sexps 1)))
(save-excursion
(while (seek-forward "(subject-p")
(forward-sexp)
(transpose-sexps 1))))

To make more modern org-modes happy. Woo.

Also add a bit of support for sibling combinators when dealing with the
implicit element, and note a problem that crops up when dealing with
selections on a non-root element (should a simple-selector select the
element, or is there an implicit descendant combinator?).