diff --git a/doc/sql.extensions/README.ddl.txt b/doc/sql.extensions/README.ddl.txt
index 42ccdb19b7..b90a9be3f3 100644
--- a/doc/sql.extensions/README.ddl.txt
+++ b/doc/sql.extensions/README.ddl.txt
@@ -244,7 +244,7 @@ alter view v_users (id, name) as
 
 Function:
 
-Makes it possible to specify non-default (which is CURRENT_USER) grantor in GRANT and REVOKE 
+Makes it possible to specify non-default (which is CURRENT_USER) grantor in GRANT and REVOKE
 commands.
 
 Syntax:
@@ -265,7 +265,7 @@ GRANT R1 TO PUBLIC GRANTED BY USER1
 GRANT R1 TO USER1 WITH ADMIN OPTION
 
 Misc:
-GRANTED BY form of clause is recommended by SQL standard. AS is supported by some other 
+GRANTED BY form of clause is recommended by SQL standard. AS is supported by some other
 servers (Informix), and is added for better compatibility.
 
 
@@ -289,18 +289,18 @@ Example:
 
 create database 'peoples.fdb'
     default character set win1252;
- 
+
 alter character set win1252
     set default collation win_ptbr;
- 
+
 create table peoples (
     id integer,
     name varchar(50)  -- will use the database default character set and the win1252 default collation
 );
- 
+
 insert into peoples values (1, 'adriano');
 insert into peoples values (2, 'ADRIANO');
- 
+
 -- will retrieve both records because win_ptbr is case insensitive
 select * from peoples where name like 'A%';
 
@@ -335,7 +335,7 @@ create database 'test.fdb'
 Function:
 
 When user is removed from security database (or any other authentication source),
-it's useful to revoke his access to any object in database. 
+it's useful to revoke his access to any object in database.
 
 Syntax:
 
@@ -392,3 +392,73 @@ ALTER { SEQUENCE | GENERATOR } <sequence name> RESTART [ WITH <value> ]
 Syntax present in 2.5 for reference:
 
 ALTER SEQUENCE <sequence name> RESTART WITH <value>
+
+
+16) Increment for sequences.
+(Claudio Valderrama)
+
+For 3.0, the options specified in (15) include INCREMENT:
+{ CREATE | RECREATE } { SEQUENCE | GENERATOR } <sequence name> [ START WITH <value> ] [ INCREMENT [BY] <increment> ]
+CREATE OR ALTER { SEQUENCE | GENERATOR } <sequence name> { RESTART | START WITH <value> } [ INCREMENT [BY] <increment> ]
+ALTER { SEQUENCE | GENERATOR } <sequence name> RESTART [ WITH <value> ] [ INCREMENT [BY] <increment> ]
+
+This is the increment that's applied to the SQL standard way of working with generators:
+NEXT VALUE FOR <sequence name>
+is equivalent to
+gen_id(<sequence name>, <increment>)
+
+The default increment for user generators is one and for system generators, zero. This makes possible
+to apply NEXT VALUE FOR <sys generator>
+since system generators cannot be changed by user requests now. Example:
+
+create sequence seq increment 10; -- starts at zero and changes by 10
+select next value for seq from rdb$database; -- result is 10
+select gen_id(seq, 1) from rdb$database; -- result is 11, gen_id() is not affected by the increment.
+
+If the database is new and no trigger has been defined, doing
+select next value for rdb$procedures from rdb$database;
+many times will produce zero again and again, because it's a system generator.
+
+The increment cannot be zero for user generators. Example:
+
+SQL> create generator g00 increment 0;
+Statement failed, SQLSTATE = 42000
+unsuccessful metadata update
+-CREATE SEQUENCE G00 failed
+-INCREMENT 0 is an illegal option for sequence G00
+
+The change in the value of INCREMENT is a feature that takes effect for each request that starts
+after the change commits. Procedures that are invoked for the first time after the change in INCREMENT
+will use the new value if they contain NEXT VALUE FOR statements. Procedures that are already
+running are not affected because they're cached. Procedures relying on NEXT VALUE FOR do not need
+to be recompiled to see the new increment, but if they are running already, they are loaded and
+no effect is seen. Of course, gen_id(gen, expression) is not affected by the increment.
+
+
+17) More security for system objects.
+(Claudio Valderrama)
+
+For 3.0, system domains cannot be altered:
+
+SQL> alter domain rdb$linger type boolean;
+Statement failed, SQLSTATE = 42000
+unsuccessful metadata update
+-ALTER DOMAIN RDB$LINGER failed
+-System domain RDB$LINGER cannot be modified
+
+The value of a system generator cannot be changed by user requests:
+
+SQL> select gen_id(rdb$procedures, 1) from rdb$database;
+               GEN_ID
+=====================
+Statement failed, SQLSTATE = 42000
+System generator RDB$PROCEDURES cannot be modified
+
+SQL> set generator rdb$procedures to 0;
+Statement failed, SQLSTATE = 42000
+unsuccessful metadata update
+-SET GENERATOR RDB$PROCEDURES failed
+-System generator RDB$PROCEDURES cannot be modified
+
+Also, the name RDB$GENERATORS does not refer anymore to an invisible system
+generator. The name can be applied to an user generator.