+ * in particular, after we set it. And then center it again.
+ * Why? I'm glad you asked. Because it doesn't actually get
+ * centered the first time; it's off by a few pixels. But then
+ * if we center it _again_, I guess we're so close to begin with
+ * that any errors aren't noticeable. Anyway, just running it
+ * twice in a row avoids a major headache. We need the wrapper
+ * because the spec says that duplicate handlers are discarded. */