+
+ /* a callback called for each entry in the tree.
+ *
+ * The arguments passed to the traverse callback are as follows:
+ *
+ * - `n` counts the number of trees being traversed.
+ *
+ * - `mask` has its nth bit set if something exists in the nth entry.
+ *
+ * - `dirmask` has its nth bit set if the nth tree's entry is a directory.
+ *
+ * - `entry` is an array of size `n` where the nth entry is from the nth tree.
+ *
+ * - `info` maintains the state of the traversal.
+ *
+ * Returning a negative value will terminate the traversal. Otherwise the
+ * return value is treated as an update mask. If the nth bit is set the nth tree
+ * will be updated and if the bit is not set the nth tree entry will be the
+ * same in the next callback invocation.
+ */