As a special exception, the Free Software Foundation gives unlimited permission to copy, distribute and modify the configure scripts that are the output of Autoconf. You need not follow the terms of the GNU General Public License when using or distributing such scripts, even though portions of the text of Autoconf appear in them. The GNU General Public License (GPL) does govern all other use of the material that constitutes the Autoconf program.

Certain portions of the Autoconf source text are designed to be copied (in certain cases, depending on the input) into the output of Autoconf. We call these the "data" portions. The rest of the Autoconf source text consists of comments plus executable code that decides which of the data portions to output in any given case. We call these comments and executable code the "non-data" portions. Autoconf never copies any of the non-data portions into its output.

This special exception to the GPL applies to versions of Autoconf released by the Free Software Foundation. When you make and distribute a modified version of Autoconf, you may extend this special exception to the GPL to apply to your modified version as well, *unless* your modified version has the potential to copy into its output some of the text that was the non-data portion of the version that you started with. (In other words, unless your change moves or copies text from the non-data portions to the data portions.) If your modification has such potential, you must delete any notice of this special exception to the GPL from your modified version.