The official DocBook documentation, version 2.4.1 resp. 3.0.

• User's Guide for the DocBook DTD by Terry Allen, Fujitsu Software Corporation, and Eve Maler, ArborText, Inc., Release 2.4.1, January 1997.
• Reference for the DocBook DTD by Terry Allen, Fujitsu Software Corporation, Eve Maler, ArborText, Inc., and Norman Walsh, O'Reilly & Associates, Inc., Release 3.0, January 1997.
• Overview of the DocBook DTD by Terry Allen, Fujitsu Software Corporation, and Eve Maler, ArborText, Inc., Release 2.4.1, January 1997.
• Customizer's Guide for the DocBook DTD by Terry Allen, Fujitsu Software Corporation, and Eve Maler, ArborText, Inc., Release 2.4.1, January 1997.