[Product-Developers] Non-open source plone plugins?

Sean Upton sdupton at gmail.com
Wed Jul 31 16:45:04 UTC 2013

On Wed, Jul 31, 2013 at 7:59 AM, Guido Stevens <guido.stevens at cosent.net> wrote:
> That clause is key. In tech-speak, not lawyerese, that normally means that
> your proprietary plugin must be able to run standalone, or against a
> compatible interface that is not Plone.

This is reasonable; moreover, APIs alone ideally should not be
copyrightable (see

>  If you write a plugin that can only
> be used as part of a Plone installation, I'd consider that a derived work
> that ought to be released under a GPLv2-compatible license.

Reciprocal obligation for something inextricably built atop Plone
seems to mean GPLv2, not just something "license-compatible".

> One can work around that by splitting the package into a "standalone"
> proprietary core logic module that does not require Plone, and a second
> GPLv2 plone integration module that requires both Plone and the proprietary
> work.
>> we license some Plone packages with licenses different from GPLv2, like
>> MIT

My employer's attorneys prefer that I release packages as MIT-licensed
when possible; I have done some lower-level libraries this way (that
only depend on Zope/ZPL and Plone BSD-licensed dependencies).  Still
most of what I release is GPL for reciprocal obligation (even if
strictly, defining a derivative work in Python is a hard problem).

For the MIT-licensed libraries, for example, I use plone.testing (BSD)
and a homemade CMFDefault layer/fixture instead of plone.app.testing
to avoid GPL dependency.

> The situation is different for utilities which are required *by* Plone, than
> it is for plugins that require Plone. utility <- Plone <- plugin

If I ever had to "productize" (for sale) something in Plone, I would
build the proprietary bits underneath, in a standalone library, and
write an integration package.  For example (not that I would do this,
but...), say I decided to write a commercial/proprietary medical
spellchecker for Plone and charge money for it and keep the terms of
distribution on the source restricted; I could do this as long as the
package/add-on integrating this into Plone was itself GPL.


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