Clarify licenses

- add license headers to everything
- convert a few files from public domain or LGPL2.1+ to GPL2+
- some archaeology to clarify which files are from which library

6 files changed, 13 insertions, 7 deletions

diff --git a/src/extension/implementation/implementation.cpp b/src/extension/implementation/implementation.cpp
index 79b2bb84c..949451293 100644
--- a/src/extension/implementation/implementation.cpp
+++ b/src/extension/implementation/implementation.cpp
@@ -1,8 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*
     Author:  Ted Gould <ted@gould.cx>
     Copyright (c) 2003-2005,2007
 
-    This code is licensed under the GNU GPL.  See COPYING for details.
+    Released under GNU GPL v2+, read the file 'COPYING' for more information.
 
     This file is the backend to the extensions system.  These are
     the parts of the system that most users will never see, but are
diff --git a/src/extension/implementation/implementation.h b/src/extension/implementation/implementation.h
index 88afa0d27..e4922a083 100644
--- a/src/extension/implementation/implementation.h
+++ b/src/extension/implementation/implementation.h
@@ -1,9 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*
     Author:  Ted Gould <ted@gould.cx>
     Copyright (c) 2003-2005,2007
 
-    This code is licensed under the GNU GPL.  See COPYING for details.
- 
+    Released under GNU GPL v2+, read the file 'COPYING' for more information.
+
     This file is the backend to the extensions system.  These are
     the parts of the system that most users will never see, but are
     important for implementing the extensions themselves.  This file
diff --git a/src/extension/implementation/script.cpp b/src/extension/implementation/script.cpp
index fe3b14093..82b6b577a 100644
--- a/src/extension/implementation/script.cpp
+++ b/src/extension/implementation/script.cpp
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /**
  * Code for handling extensions (i.e. scripts).
  *
@@ -9,7 +10,7 @@
  *
  * Copyright (C) 2002-2007 Authors
  *
- * Released under GNU GPL, read the file 'COPYING' for more information
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
  */
 
 #include <glibmm.h>
diff --git a/src/extension/implementation/script.h b/src/extension/implementation/script.h
index fba1df136..9a3b40278 100644
--- a/src/extension/implementation/script.h
+++ b/src/extension/implementation/script.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Code for handling extensions (i.e., scripts)
  *
@@ -7,7 +8,7 @@
  *
  * Copyright (C) 2002-2005 Authors
  *
- * Released under GNU GPL, read the file 'COPYING' for more information
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
  */
 
 #ifndef INKSCAPE_EXTENSION_IMPEMENTATION_SCRIPT_H_SEEN
diff --git a/src/extension/implementation/xslt.cpp b/src/extension/implementation/xslt.cpp
index f50124e09..7d4bff11a 100644
--- a/src/extension/implementation/xslt.cpp
+++ b/src/extension/implementation/xslt.cpp
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /** \file
  * Code for handling XSLT extensions.
  */
@@ -9,7 +10,7 @@
  *
  * Copyright (C) 2006-2007 Authors
  *
- * Released under GNU GPL, read the file 'COPYING' for more information
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
  */
 
 #include <glibmm/fileutils.h>
diff --git a/src/extension/implementation/xslt.h b/src/extension/implementation/xslt.h
index eb24436ae..f4fc871a9 100644
--- a/src/extension/implementation/xslt.h
+++ b/src/extension/implementation/xslt.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Code for handling XSLT extensions
  *
@@ -6,7 +7,7 @@
  *
  * Copyright (C) 2006-2007 Authors
  *
- * Released under GNU GPL, read the file 'COPYING' for more information
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
  */
 
 #ifndef __INKSCAPE_EXTENSION_IMPEMENTATION_XSLT_H__