this is obsolete and lives in matrix-doc in specification/30_server_server_api.rst now

docs/server-server/protocol-format.rst

-
-Transaction
-===========
-
-Required keys:
-
-============ =================== ===============================================
-    Key            Type                         Description
-============ =================== ===============================================
-origin       String              DNS name of homeserver making this transaction.
-ts           Integer             Timestamp in milliseconds on originating 
-                                 homeserver when this transaction started.
-previous_ids List of Strings     List of transactions that were sent immediately
-                                 prior to this transaction.
-pdus         List of Objects     List of updates contained in this transaction.
-============ =================== ===============================================
-
-
-PDU
-===
-
-Required keys:
-
-============ ================== ================================================
-    Key            Type                         Description
-============ ================== ================================================
-context      String             Event context identifier
-origin       String             DNS name of homeserver that created this PDU.
-pdu_id       String             Unique identifier for PDU within the context for
-                                the originating homeserver.
-ts           Integer            Timestamp in milliseconds on originating 
-                                homeserver when this PDU was created.
-pdu_type     String             PDU event type.
-prev_pdus    List of Pairs      The originating homeserver and PDU ids of the
-             of Strings         most recent PDUs the homeserver was aware of for
-                                this context when it made this PDU.
-depth        Integer            The maximum depth of the previous PDUs plus one.
-============ ================== ================================================
-
-Keys for state updates:
-
-================== ============ ================================================
-    Key               Type                      Description
-================== ============ ================================================
-is_state           Boolean      True if this PDU is updating state.
-state_key          String       Optional key identifying the updated state within
-                                the context.
-power_level        Integer      The asserted power level of the user performing
-                                the update.
-min_update         Integer      The required power level needed to replace this
-                                update.
-prev_state_id      String       The homeserver of the update this replaces
-prev_state_origin  String       The PDU id of the update this replaces.
-user               String       The user updating the state.
-================== ============ ================================================
-
-
-
-