+
+ /* If set, missing messages are stored in ghost mail documents.
+ * If unset, thread IDs of ghost messages are stored as database
+ * metadata instead of in ghost documents.
+ *
+ * Introduced: version 3. */
+ NOTMUCH_FEATURE_GHOSTS = 1 << 4,
+
+
+ /* If set, then the database was created after the introduction of
+ * indexed mime types. If unset, then the database may contain a
+ * mixture of messages with indexed and non-indexed mime types.
+ *
+ * Introduced: version 3. */
+ NOTMUCH_FEATURE_INDEXED_MIMETYPES = 1 << 5,
+
+ /* If set, messages store the revision number of the last
+ * modification in NOTMUCH_VALUE_LAST_MOD.
+ *
+ * Introduced: version 3. */
+ NOTMUCH_FEATURE_LAST_MOD = 1 << 6,