[wp-docs] GPL requirement on Writing_a_Plugin

[michael at followingedge.com]

Since I had last read the "Writing a Plugin" page...

http://codex.wordpress.org/Writing_a_Plugin

...almost a year ago, the following sentence has been added to the "Plugin 
File Structure" section:

   You do not need to license your plugin under the terms of the GPL;
   but any license you choose to use <strong>must</strong> be
   compatible with the GPL.

I think this is incorrect. Probably, it is a misunderstanding from the GPL 
FAQ that addresses how programs with restrictive license plug-ins cannot be 
distributed as a combined work.

Obviously, if a person writes a plug-in from scratch (as opposed to using 
existing GPL, or otherwise, licensed code) and uses the public WordPress 
API, the plug-in copyright rests completely with the author and the GPL 
doesn't have any avenue to impel the author to license the plug-in under 
GPL, or any other license. Obviously, the author could not combine the 
plug-in with WordPress and distribute them together, since that would 
violate the WordPress GPL license for distribution. But, the author could 
distribute the plug-in separately under any license, and licensed users 
could install the plug-in on their WordPress installation, creating a 
"combined work" for their own use, within the WordPress GPL license.

I think it would be less grating to generous authors to encourage them to 
distribute their plug-in under the GPL or other open-source licenses, 
rather than try and force them to do so. Trying to force generosity might 
be taken the wrong way. I know that's the way I felt when I saw the new 
sentence. Encouraging GPL licensing by appealing to authors' 
community-minded generosity and via other perks (like hosting on 
wp-plugins.org) might come across better, and be more accurate.

-Michael
michael at followingedge.com