Markdown licensing

[Michel Fortin]

I'm not sure either about this license change. So here is my take on it.

Whatever the license, I believe it requires more explanation that what 
we have now. As many said, things are not so easy to understand when it 
comes to the GPL. I took me some time to investigate this subject a 
while ago as someone asked me if the GPL would prohibit the use of PHP 
Markdown in a private project.

I wrote the following as an answer. Read on...

* * *

How to include PHP Markdown in non-GPL software
-----------------------------------------------

First, you can use it under the terms of the GPL, but that does not 
mean you have to: you are always free to contact the copyright holders 
(John Gruber and me in that case) and ask for a specific permission to 
use the program inside yours. If you intend to make profit out of it, 
we will likely ask for some money in exchange.

Second, the GPL mostly require that you give the right to see, modify 
and redistribute the source code -- all this free of charge -- to 
anyone you give the software to. If you do not release your software to 
anyone you are not required to give the source to anyone.

If you do distribute to some people the proprietary program, things 
gets a little more tricky. Here are two scenarios:

1.	PHP Markdown is included as a plugin. This means you can
	safely remove it without much trouble from the distribution
	and it only remove the ability to do what is in that file
	(Markdown text formatting). The Markdown plugin included may
	have been modified from the original, in which case the new
	version is released under GPL but the rest of the program is
	not.

2.	PHP Markdown is a core component of your software. Part of
	your software depend on it to work correctly. In that case
	your program is a derived work that should be licensed under
	GPL.

If scenario 1 and 2 are not possible, you should ask John and me about 
an agreement specific to your program.

This was in part inspired by this page:
<http://www.gnu.org/licenses/gpl-faq.html#GPLInProprietarySystem>

* * *

Of course, you could replace "proprietary program" with "BSD-licensed 
software". Make sure you read the question-answer from the official GPL 
FAQ linked above.

About the "include" thing in PHP, if you write this in a proprietary 
program:

	if (file_exists("markdown.php") {
		include "markdown.php";
		$text = Markdown($text);
	}
	else {
		/* Do nothing, $text must be HTML already. */
	}

Then it's a plugin system -- rather simple, but it can still work 
without PHP Markdown -- and there is no need to bother about the 
licensing of Markdown. At least, this is the way I see it.


Michel Fortin
michel.fortin at michelf.com
http://www.michelf.com/