Licensing
The terms of the GNU General Public License (GPL) state that the Emacs source code, including both the C and Emacs Lisp components, are freely available for examination, modification, and redistribution.
For GNU Emacs (and many other GNU packages), it remains policy to accept significant code contributions only if the copyright holder executes a suitable disclaimer or assignment of their copyright interest to the Free Software Foundation, although one exception to this policy occurred in the case of MULE (MULtilingual Extension, which handles Unicode and more advanced methods of dealing with other languages' scripts) code, since the copyright holder (the Japanese government) could not assign copyright. This does not apply to extremely minor code contributions of less than 10 lines, or to bug fixes. This policy is in place so that FSF can defend the software in court if its copyleft licence is violated.
Older versions of the GNU Emacs documentation appeared under an ad-hoc license which required the inclusion of certain text in any modified copy. In the GNU Emacs user's manual, for example, this included how to obtain GNU Emacs and Richard Stallman's essay The GNU Manifesto. The XEmacs manuals, which were inherited from older GNU Emacs manuals when the fork occurred, have the same license. Newer versions of the documentation use the GNU Free Documentation License and makes use of "invariant sections" to require the inclusion of the same documents, additionally requiring that the manuals proclaim themselves as GNU Manuals.
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