Proper ZCML tree for Zope 2.10
------------------------------

:Author: Philipp von Weitershausen, philikon@philikon.de
:Status: IsDraftProposal


Current situation
-----------------

Currently, ZCML initialization takes place as follows:

1. Zope initializes, among others, the Five product by calling
   ``Products.Five.initialize``::

     def initialize(context):
         zcml.load_site()

2. ``Products.Five.zcml.load_site`` checks whether
   ``$INSTANCE/etc/site.zcml`` exists.  If not, it will fall back to
   ``Products/Five/skel/site.zcml`` which will be the case most of the
   time because many Zope 2 developers, even though they might use
   Five features, do not bother to copy the ``skel`` directory below
   Five to their instance home.

3. As the first thing it does, ``site.zcml`` includes
   ``Products/Five/configure.zcml``::

     <include package="Products.Five" />

   This way, all directive handlers other than the basic ones are
   registered as well as all the essential and not-so-essential
   components that Five registers.

4. ``site.zcml`` then goes on including Zope 3-style package includes::

     <include files="package-includes/*-meta.zcml" />
     <include files="package-includes/*-configure.zcml" />

   In the ``Products/Five/skel`` directory, ``package-includes`` is
   empty.  But when the ``skel`` directory is copied to the instance
   home, it can serve as a place to put ZCML slugs, just like in Zope
   3 instances.

5. Finally, ``site.zcml`` ends with including product configuration::

     <five:loadProducts />
     <five:loadProductsOverrides />

   This will automatically find all installed products and search in
   them for ``configure.zcml`` files and ``overrides.zcml`` files,
   respectively.  If these files exist, they are loaded.  The Five
   product's configuration is not loaded again as ZCML won't load any
   files twice.

Summary:

I) The initialization of the Five product takes care of starting the
   ZCML configuration tree.

II) Products can simply be dropped in and their ZCML configuration is
    picked up automatically.  This corresponds to the product
    deployment scheme Zope 2 developers are used to.

III) Other Python packages need to be explicitly included by a ZCML
     slug.  This corresponds to the Zope 3 scheme of deploying
     packages.


Problem
-------

Only point I) from above is the problem.  In fact, this proposal does
not question the practice of points II) and III).

Five 1.2 for the first time introduced ZCML that is not about Five
anymore but about the Zope 2 core (mostly the OFS package).  These
ZCML declarations should really be in the packages they are about, not
in Five.



Proposal
--------

This proposal is NOT about changing the automatic configuration of
Products.

XXX

zopeschema.xml 

Zope2.App.startup:

zope.app.appsetup.config(options.site_definition, features=features)
probably more like Products.Five.zcml.load_site()


notify(zope.app.appsetup.interfaces.DatabaseOpened(DB))


Risks
-----

XXX