+
+----
+
+I implemented the above in a branch.
+[[!template id=gitbranch branch=origin/dependency-types author="[[joey]]"]]
+
+Then I found some problems:
+
+* pagestats is often used with a pagespec that uses `tagged()`.
+ A pure contentless dependency does not work for that, it needs to look
+ at link info.
+* orphans and brokenlinks cannot use contentless dependencies because they
+ need to update when links change.
+* Something simple like pagecount, that seems like it could use a
+ contentless dependency, can have a pagespec that uses metadata, like
+ `author()` or `copyright()`.
+
+Now I'm thinking about having a contentless dependency look at page
+metadata, and fire if the metadata changes. And it seems links should
+either be included in that, or there should be a way to make a dependency
+that fires when a page's links change. (And what about backlinks?)
+
+It's easy to see when a page's links change, since there is `%oldlinks`.
+To see when metadata is changed is harder, since it's stored in the
+pagestate by the meta plugin.
+
+(Alternative: Make add_depends look at the pagespec. Ie, if it is a simple
+page name, or a glob, we know a contentless dependency can be valid.
+If's more complex, convert the dependency from contentless to full. Finding
+a non-ad-hoc, non-sucky way to do that could be hard.)