itself, but treated as a license interpretation matter by the FSF) held that GPLv2 allowed such

combinations only if the non-GPL licensing terms permitted distribution under

the GPL and imposed no restrictions on the code that were not also imposed by

the GPL\@.  In practice, the FSF historically supplemented that policy with a structure of

exceptions for certain kinds of combinations.

GPLv3~\S7  implements a more explicit policy on license

compatibility.  It formalizes the circumstances under which a licensee may

release a covered work that includes an added part carrying non-GPL terms. 

GPLv3~\S7 distinguish between terms that provide additional permissions, and terms that

place additional requirements on the code, relative to the permissions and

requirements established by applying the GPL to the code.

As discussed in the previous section of this tutorial, GPLv3~\S7 first and foremost explicitly allows added parts covered by terms with

additional permissions to be combined with GPL'd code. This codifies the

existing practice of regarding such licensing terms as compatible with the

GPL\@. A downstream user of a combined GPL'd work who modifies such an added

part may remove the additional permissions, in which case the broader

permissions no longer apply to the modified version, and only the terms of

the GPL apply to it.

In its treatment of terms that impose additional requirements, GPLv3\S7

extends the range of licensing terms with which the GPL is compatible.  An

added part carrying additional requirements may be combined with GPL'd code,

ensures that enhanced license compatibility does not

defeat the broader software-freedom-defending terms of the GPL\@. Unlike terms that grant

additional permissions, terms that impose additional requirements cannot be

removed by a downstream user of the combined GPL'd work, because only in the

pathological case\footnote{Theoretically, a user could collect copyright

  assignment from all known contributors and then do this, but this would

  indeed be the pathological case.}  would a user have the right to do so.

In general, the types of additional requirements were those terms in regular

use by other non-copyleft Free Software licenses that the FSF found

unobjectionable.  The specific details GPLv3's permitted additional

requirements hat GPLv3 are as follows:

\begin{enumerate}[label=7(\alph*):,ref=GPLv3s7\alph*]

\item This provision allows alternative ``disclaimer of warranty''

  forms. Copyright holders can disclaim warranty or limit liability

  differently from the terms as provided under GPLv3\S~\S15--16.  Drafters

  included this permission to advance the internationalization goals of

  GPLv3; international treaties lack adequate harmonization for laws

  regarding warranty and disclaimer.

\item This provision allows alternative requirements for preservation of

  appropriate legal notices.  GPLv3 permits additional requirements regarding