;; Render empty XHTML tags with an HTML-compatible close tag.
;; For HTML compatibility, EMPTY elements (according to DTD) should always
;; use the <br /> form, and non-EMPTY elements should use the close-tag form.
;; From http://www.w3.org/TR/xhtml1/#guidelines:

;; C.2 Include a space before the trailing / and > of empty elements,
;; e.g. <br />, <hr /> and <img src="karen.jpg" alt="Karen" />.
;; C.3 Also, use the minimized tag syntax for empty elements, e.g.
;; <br />, as the alternative syntax <br></br> allowed by XML gives
;; uncertain results in many existing user agents.

;; These elements use the minimized close tag form; all others will have
;; an explicit close tag.
(define xhtml-empty-elements '(base meta link hr br param img area input col))
;; These open tags will not have a newline prefixed, so as not to
;; introduce extraneous whitespace.
(define xhtml-inline-elements '(a abbr acronym b bdo bdi big blink cite code dfn del
                                em font i img ins kbd q s samp small span strike
                                strong sub sup tt u var 
                                button input label select textarea
                                ;; HTML5
                                audio canvas command date keygen mark meter output progress
                                rp rt ruby time video
                                ))

(define (entag-xhtml tag elems)
  (let ((entagged-result
         (if (and (pair? elems) (pair? (car elems))
                  (eq? '@ (caar elems)))
             (list #\< tag (cdar elems)
                   (if (pair? (cdr elems))
                       (list #\> (cdr elems) "</" tag #\>)
                       (if (memq tag xhtml-empty-elements)
                           " />"
                           (list #\> "</" tag #\>))))
             (list #\< tag
                   (if (pair? elems)
                       (list #\> elems "</" tag #\>)
                       (if (memq tag xhtml-empty-elements)
                           " />"
                           (list #\> "</" tag #\>)))))))

    (if (memq tag xhtml-inline-elements)
        entagged-result
        (cons #\newline entagged-result))))