promise when
necessary, is the code's <em class="firstterm">forkability</em>: the
ability of anyone to take a copy of the source code and use it to
start a competing project, known as a <em class="firstterm">fork</em>.
The paradoxical thing is that the <span class="emphasis"><em>possibility</em></span> of
forks is usually a much greater force in free software projects than
actual forks, which are very rare.  Because a fork is bad for everyone
(for reasons examined in detail in
<a class="xref" href="ch08s06.