◊(Local Yarn Code "Check-in [63baf301]")

}|

The @code{url} tag for a given identifier may be placed anywhere in the document, even before it is
referenced. If you create a @code{link} for an identifier that has no corresponding @code{url},
a @code{"Missing reference: [link-id]"} message will be substituted for the URL. Conversely, 
creating a @code{url} that is never referenced will produce no output and no warnings or errors.

}

@defproc*[([(xref [title string?]) txexpr?]
           [(xref [article-base string?] [element xexpr?] ...) txexpr?])]{

Hyperlink to another article within @italic{The Local Yarn} using an @racket[_article-base], which
is the base filename only of an @tech{article} within @racket[articles-folder] (without the
@filepath{.poly.pm} extension).

If a single argument is supplied (@racket[_title]) it is typeset italicized as the link text, and
its @racket[normalize]d form is used as the article base to generate the link. If more than one
argument is supplied, the first is used as the article base, and the rest are used as the contents
of the link.

@codeblock|{
  #lang pollen

  A link to ◊xref{My Ultimate Article} will link to “my-ultimate-article.poly.pm”.
  A link using ◊xref["my-ultimate-article"]{this form} goes to the same place.
}|

}

@deftogether[(@defproc[(figure     [image-file string?] [caption xexpr?] ...) txexpr?]
              @defproc[(figure-@2x [image-file string?] [caption xexpr?] ...) txexpr?])]{

Insert a block-level image. The @racket[_image-file] should be supplied as a filename only, with no
folder names. It is assumed that the image is located inside an @racket[images-folder] within the

  (cond [(eq? (get-tag tx) 'link&)
         (let* ([url-ref (attr-ref tx 'ref)]
                [url (or (hash-ref link-urls url-ref #f)
                         (format "Missing reference: ~a" url-ref))])
           `(a [[href ,url]] ,@(get-elements tx)))]
        [else tx]))

;; Quick link to another article
(define (html-xref . elems)
  `(a [[href ,(format "~aarticles/~a.html" web-root (first elems))]
       [class "xref"]]
      ,@(rest elems)))
;; Fast link to another article
(define html-xref
  (case-lambda
    [(title) `(a [[href ,(format "~aarticles/~a.html" web-root (normalize title))]
                  [class "xref"]]
                 (i ,title))]
    [elems `(a [[href ,(format "~aarticles/~a.html" web-root (first elems))]
                [class "xref"]]
               ,@(rest elems))]))

;; Footnotes
;;
;; Private use:
(define fn-names null)
(define fn-definitions (make-hash))
(define (fn-id x) (here-id (string-append x "_fn")))