first sentence of GPLv3\S4\P2.  The GPLv2\S1\P1 means that the GPL permits

one to charge money for the distribution of software.  Despite efforts by

copyleft advocates to explain this in GPLv2 itself and in other documents,

there are evidently some people who still believe that GPLv2 allows charging

for services but not for selling copies of software and/or that the GPL

requires downloads to be gratis.  Perhaps this is because GPLv2 referred to

charging a ``fee''; the term ``fee'' is generally used in connection with

services.

GPLv2's wording also referred to ``the physical act of transferring.''  The

intention was to distinguish charging for transfers from attempts to impose

licensing fees on all third parties.  ``Physical'' might be read, however, as

suggesting ``distribution in a physical medium only''.

To address these two issues, GPLv3 says ``price'' in place of ``fee,'' and

removes the term ``physical.''

GPLv3~\S4 has also been revised from its corresponding section in GPLv2 in

light of the GPLv3~\S7 (see \S~\ref{GPLv3s7} in this tutorial for more).

Specifically, a distributor of verbatim copies of the program's source code

must obey any existing additional terms that apply to parts of the program

pursuant to GPLv3~\S7.  In addition, the distributor is required to keep

intact all license notices, including notices of such additional terms.

\section{GPLv3~\S5: Modified Source}

\label{GPLv3s5}

% FIXME: 5(a) is slightly different in final version

Section 5 contains a number of changes relative to the corresponding section

in GPLv2. Subsection 5a slightly relaxes the requirements regarding notice of

changes to the program. In particular, the modified files themselves need no

longer be marked. This reduces administrative burdens for developers of

modified versions of GPL'd software.

Under subsection 5a, as in the corresponding provision of GPLv2, the notices

must state ``the date of any change,'' which we interpret to mean the date of

one or more of the licensee's changes.  The best practice would be to include

the date of the latest change.  However, in order to avoid requiring revision

of programs distributed under ``GPL version 2 or later,'' we have retained

the existing wording.

% FIXME:  It's now (b) and (c).  Also, ``validity'' of proprietary

%         relicensing?  Give me a break.  I'll fix that.

Subsection 5b is the central copyleft provision of the license.  It now

states that the GPL applies to the whole of the work.  The license must be