Mon Jan  4 07:06:50 UTC 2010  pix@kepibu.org
  * Support for asking about ancestors under lhtml
diff -rN -u old-Oh, Ducks!/notes new-Oh, Ducks!/notes
--- old-Oh, Ducks!/notes	2015-10-13 02:13:20.000000000 +0000
+++ new-Oh, Ducks!/notes	2015-10-13 02:13:20.000000000 +0000
@@ -129,9 +129,11 @@
 I also recommend submitting a patch.  Other people might want to use
 that selector, too!
 * To Do
-** working lhtml/xmls support [1/2]
+** working lhtml/xmls support [2/2]
  * [X] non-descendant cases (class, id, etc.)
- * [ ] selectors involving descendants
+ * [X] selectors involving descendants
+   CAUTION: Won't produce sane results if the document tree is
+            modified or you use nested (match)es.
 ** write documentation
 ** improve selector support
 *** positional selectors [11/11]
diff -rN -u old-Oh, Ducks!/traversal/lhtml.lisp new-Oh, Ducks!/traversal/lhtml.lisp
--- old-Oh, Ducks!/traversal/lhtml.lisp	2015-10-13 02:13:20.000000000 +0000
+++ new-Oh, Ducks!/traversal/lhtml.lisp	2015-10-13 02:13:20.000000000 +0000
@@ -3,18 +3,44 @@
 ;;;          structurally compatible).  Sorry, but that's the way it goes.
 (in-package #:oh-ducks.traversal)
 
+(defvar *lhtml-family-tree* nil)
+
+(defun in-hash (key hash)
+  (multiple-value-bind (val present-p) (gethash key hash)
+    (declare (ignore val))
+    present-p))
+
+(defun %mark-parents (parent children)
+  (dolist (item children)
+    (setf (gethash item *lhtml-family-tree*) parent)
+    (%mark-parents item (element-children item))))
+
+;; WARNING: This won't produce sane results for nested (match)es, because we
+;;          have no way to bind in a large enough scope.
+(defmethod unify:unify ((template oh-ducks::css-selector-template)
+                        (element list)
+                        &optional (env (unify:make-empty-environment))
+                        &key)
+  (if (and *lhtml-family-tree*
+	   (in-hash element *lhtml-family-tree*))
+      (call-next-method)
+      (let ((*lhtml-family-tree* (make-hash-table :test 'eq)))
+        (%mark-parents nil (list element))
+        (%mark-parents element (element-children element))
+        (call-next-method))))
+
 ;;; general accessors
 
 (defmethod element-children ((element list))
   (remove-if-not (lambda (x) (and (listp x) (keywordp (car x))))
                  (cddr element)))
 
-;; FIXME: bleh... may not even be worth trying to support this
 (defmethod element-parent ((element list))
-  (error "cannot get parent"))
-
-(defmethod element-ancestors ((element list))
-  (error "cannot get ancestors"))
+  (multiple-value-bind (parent present?)
+      (gethash element *lhtml-family-tree*)
+    (if present?
+        parent
+        (error "unable to determine parent"))))
 
 (defmethod element-attribute ((attribute symbol) (element list))
   (cadr (assoc attribute (cadr element))))