Clarify the logical view of iterators

include/VersionedMap.h

@@ -86,10 +86,12 @@ struct VersionedMap {
   /** The version of the most recent call to `setOldestVersion`. */
   int64_t getOldestVersion() const;
 
-  /** Fixed to a specific version. It's thread-safe to operate on an iterator
-   * concurrently with any method of `VersionedMap`, as long as it's not
-   * invalidated by `setOldestVersion`. @warning must not outlive its
-   * `VersionedMap`. */
+  /** Iterates through a canonicalized view of all the mutations from
+   * `oldestVersion` to the iterator's version. There may be mutations from
+   * versions < `oldestVersion`, but they won't affect the result. It's
+   * thread-safe to operate on an iterator concurrently with any method of
+   * `VersionedMap`, as long as it's not invalidated by `setOldestVersion`.
+   * @warning must not outlive its `VersionedMap`. */
   struct Iterator {
 
     Iterator() = default;