Added `split-attributes+body', to make it easy to write xml-like wrapper

functions, and used it in `center-div'.

collects/meta/web/common/extras.rkt

@@ -10,9 +10,11 @@
 ;; a div that is centered, but the text is still left-justified
 (provide center-div)
 (define (center-div . text)
-  (div align: 'center
-       (div align: 'left style: "display: inline-block;"
-            text)))
+  (let-values ([(attrs body) (split-attributes+body text)])
+    (apply div align: 'center
+           (append attrs
+                   (list (div align: 'left style: "display: inline-block;"
+                              body))))))
 
 ;; a grayish tt text
 (provide TT)

collects/meta/web/html/xml.rkt

@@ -37,6 +37,15 @@
                                      "missing attribute value for `~s:'" a)]
             [else (loop (cddr xs) (cons (cons a (cadr xs)) as))]))))
 
+;; similar, but keeps the attributes as a list, useful to build new functions
+;; that accept attributes without knowing about the xml structs.
+(provide split-attributes+body)
+(define (split-attributes+body xs)
+  (let loop ([xs xs] [as '()])
+    (if (and (pair? xs) (pair? (cdr xs)) (attribute->symbol (car xs)))
+      (loop (cddr xs) (list* (cadr xs) (car xs) as))
+      (values (reverse as) xs))))
+
 ;; ----------------------------------------------------------------------------
 ;; An output that handles xml quoting, customizable