4.9 What is different about Emacs 23?

Other changes include: support for serial port access; D-Bus bindings; a new Visual Line mode for line-motion; improved completion; a new mode (‘DocView’) for viewing of PDF, PostScript, and DVI documents; nXML mode (for editing XML documents) is included; VC has been updated for newer version control systems; etc.

Consult the Emacs NEWS.23 file for the full list of changes in Emacs 23.