first, but potentially having less testing, stability and security. The developers released version 20.0 on 9 February 1997, and version 21.0 on 12 July 1998. As of January 2009, the stable branch had reached version 21.4.22 and the beta branch version 21.5.28. No gamma releases exist . With the release of XEmacs 21.4.0, version numbers follow a scheme whereby an odd second number signals a development-version, and an even second number indicates a stable release. XEmacs and GNU Emacs Several of XEmacs's principal developers have published accounts of the split between XEmacs and GNU Emacs, for example, Stephen Turnbull's summary of the arguments from both sides. One of the main disagreements involves different views of copyright assignment. The FSF sees copyright assignment to the FSF as necessary to allow it to defend the code against GPL violations, while the XEmacs developers have argued that the lack of copyright assignment has allowed major companies to get involved, as sometimes companies can license their code but due to a cautious attitude concerning fiduciary duties to shareholders, companies may have trouble in getting permission to assign away code completely. The Free Software Foundation holds copyright of much of the XEmacs code because of prior copyright assignment during merge attempts and cross-development. Whether a piece of new XEmacs code enters GNU Emacs often depends on the willingness of that individual contributor to assign the code to the FSF. New features in either editor usually show up in the other sooner or later. Furthermore, many developers contribute to both projects. The XEmacs project has a policy of maintaining compatibility with the GNU Emacs API. For example, it provides a compatibility-layer implementing overlays via the native extent functionality. "XEmacs developers strive to keep their code compatible with GNU Emacs, especially on the Lisp level." As XEmacs development has slowed, XEmacs has incorporated much code from GNU Emacs, while GNU Emacs has implemented many formerly XEmacs-only features. This has led some users to proclaim XEmacs' death, advocating that its developers contribute to GNU Emacs instead. Many major packages, such as Gnus and Dired, were formerly developed to work with both, although the main developer of Gnus has announced his intention to move the Gnus tree into the main Emacs trunk and remove XEmacs compatibility code, citing other packages similarly dropping XEmacs support. In December 2015 project maintainer Stephen J. Turnbull posted a message to an XEmacs development