This Program is intended to be used with and modify existing code (the "Modded Code") and to build a robust modding community with open source principles. The purpose of this exception is to address issues when an open source modding community interacts with potentially proprietary code. In addition, the modding community often uses libraries (the "Modding Libraries") under licenses that may be incompatible with the GPL ("Modding Library Licenses").
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Modding Exception
In addition, as a special exception, the authors gives You the additional right to link the code of this Program with the existing code that this Program is intended to be used with or modify and to distribute linked combinations including the two, subject to the limitations in this paragraph. Modded Code permitted under this exception may link to the code of this Program without causing the Modded Code and portion of the combined work corresponding to the Modded Code to be covered by the GNU General Public License. You must obey the GNU General Public License in all respects for all of the Program code and other code used in conjunction with the Program except the Modded Code covered by this exception. If you modify this file, you may extend this exception to your version of the file, but you are not obligated to do so. If you do not wish to provide this exception without modification, you must delete this exception statement from your version and license this file solely under the GPL without exception.
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GPL-3.0 Linking Exception (with Corresponding Source)
Additional permission under GNU GPL version 3 section 7
If you modify this Program, or any covered work, by linking or combining it with Modding Libraries (or a modified version thereof), containing parts covered by the terms of Modding Library Licenses, the licensors of this Program grant you additional permission to convey the resulting work. Corresponding Source for a non-source form of such a combination shall include the source code for the parts of Modding Libraries used as well as that of the covered work.