break out 'extending config' into exconfig and add stuff about the action method; move startup and router chapters to earlier in toc

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+.. index::
+   single: extending configuration
+
+.. _extconfig_narr:
+
+Extending Pyramid Configuration
+===============================
+
+Pyramid allows you to extend its Configurator with custom directives.  These
+directives can add an :term:`action`, participate in :term:`conflict
+resolution`, and can provide some number of :term:`introspectable` objects.
+
+.. index::
+   single: add_directive
+   pair: configurator; adding directives
+
+.. _add_directive:
+
+Adding Methods to the Configurator via ``add_directive``
+--------------------------------------------------------
+
+Framework extension writers can add arbitrary methods to a
+:term:`Configurator` by using the
+:meth:`pyramid.config.Configurator.add_directive` method of the configurator.
+Using :meth:`~pyramid.config.Configurator.add_directive` makes it possible to
+extend a Pyramid configurator in arbitrary ways, and allows it to perform
+application-specific tasks more succinctly.
+
+The :meth:`~pyramid.config.Configurator.add_directive` method accepts two
+positional arguments: a method name and a callable object.  The callable
+object is usually a function that takes the configurator instance as its
+first argument and accepts other arbitrary positional and keyword arguments.
+For example:
+
+.. code-block:: python
+   :linenos:
+
+   from pyramid.events import NewRequest
+   from pyramid.config import Configurator
+
+   def add_newrequest_subscriber(config, subscriber):
+       config.add_subscriber(subscriber, NewRequest).
+
+   if __name__ == '__main__':
+       config = Configurator()
+       config.add_directive('add_newrequest_subscriber',
+                            add_newrequest_subscriber)
+
+Once :meth:`~pyramid.config.Configurator.add_directive` is called, a user can
+then call the added directive by its given name as if it were a built-in
+method of the Configurator:
+
+.. code-block:: python
+   :linenos:
+
+   def mysubscriber(event):
+       print event.request
+
+   config.add_newrequest_subscriber(mysubscriber)
+
+A call to :meth:`~pyramid.config.Configurator.add_directive` is often
+"hidden" within an ``includeme`` function within a "frameworky" package meant
+to be included as per :ref:`including_configuration` via
+:meth:`~pyramid.config.Configurator.include`.  For example, if you put this
+code in a package named ``pyramid_subscriberhelpers``:
+
+.. code-block:: python
+   :linenos:
+
+   def includeme(config)
+       config.add_directive('add_newrequest_subscriber',
+                            add_newrequest_subscriber)
+
+The user of the add-on package ``pyramid_subscriberhelpers`` would then be
+able to install it and subsequently do:
+
+.. code-block:: python
+   :linenos:
+
+   def mysubscriber(event):
+       print event.request
+
+   from pyramid.config import Configurator
+   config = Configurator()
+   config.include('pyramid_subscriberhelpers')
+   config.add_newrequest_subscriber(mysubscriber)
+
+Using ``config.action`` in a Directive
+--------------------------------------
+
+If a custom directive can't do its work exclusively in terms of existing
+configurator methods (such as
+:meth:`pyramid.config.Configurator.add_subscriber`, as above), the directive
+may need to make use of the :meth:`pyramid.config.Configurator.action`
+method.  This method adds an entry to the list of "actions" that Pyramid will
+attempt to process when :meth:`pyramid.config.Configurator.commit` is called.
+An action is simply a dictionary that includes a :term:`discriminator`,
+possibly a callback function, and possibly other metadata used by Pyramid's
+action system.
+
+Here's an example directive which uses the "action" method:
+
+.. code-block:: python
+   :linenos:
+
+   def add_jammyjam(config, jammyjam):
+       def register():
+           config.registry.jammyjam = jammyjam
+       config.action('jammyjam', register)
+
+   if __name__ == '__main__':
+       config = Configurator()
+       config.add_directive('add_jammyjam', add_jammyjam)
+
+Fancy, but what does it do?  The action method accepts a number of arguments.
+In the above directive named ``add_jammyjam``, we call
+:meth:`~pyramid.config.Configurator.action` with two arguments: the string
+``jammyjam`` is passed as the first argument, ``discriminator`` and the
+closure function named ``register`` is passed as the second argument,
+named ``callable``.
+
+When the :meth:`~pyramid.config.Configurator.action` method is called, it
+appends an action to the list of pending configuration actions.  All pending
+actions with the same discriminator value are potentially in conflict with
+one another (see :ref:`conflict_detection`).  When the
+:meth:`~pyramid.config.Configurator.commit` method of the Configurator is
+called (either explicitly or as the result of calling
+:meth:`~pyramid.config.Configurator.make_wsgi_app`), conflicting actions are
+potentially automatically resolved as per
+:ref:`automatic_conflict_resolution`.  If a conflict cannot be automatically
+resolved, a ConfigurationConflictError is raised and application startup is
+prevented.
+
+In our above example, therefore, if a consumer of our ``add_jammyjam``
+directive did this:
+
+.. code-block:: python
+   :linenos:
+
+   config.add_jammyjam('first')
+   config.add_jammyjam('second')
+
+When the action list was committed, the user's application would not start,
+because the discriminators of the actions generated by the two calls are in
+direct conflict.  Automatic conflict resolution cannot resolve the conflict,
+and the user provided no intermediate
+:meth:`pyramid.config.Configurator.commit` call between the calls to
+``add_jammyjam`` to ensure that the successive calls did not conflict with
+each other.  This is the purpose of the discriminator argument to the action
+method: it's used to indicate a uniqueness constraint for an action.  Two
+actions with the same discriminator will conflict unless the conflict is
+automatically or manually resolved. A discriminator can be any hashable
+object, but it is generally a string or a tuple.
+
+But let's imagine that a consumer of ``add_jammyjam`` used it in such a way
+that no configuration conflicts are generated.
+
+.. code-block:: python
+   :linenos:
+
+   config.add_jammyjam('first')
+
+What happens then?  When the ``add_jammyjam`` method is called, an action is
+appended to the pending actions list.  When the pending configuration actions
+are processed during :meth:`~pyramid.config.Configurator.commit`, and no
+conflicts occur, the *callable* provided as the second argument to the
+:meth:`~pyramid.config.Configurator.action` method within ``add_jammyjam`` is
+called with no arguments.  The callable in ``add_jammyjam`` is the
+``register`` closure function.  It simply sets the value
+``config.registry.jammyjam`` to whatever the user passed in as the
+``jammyjam`` argument to the ``add_jammyjam`` function.  Therefore, the
+result of the user's call to our directive will set the ``jammyjam``
+attribute of the registry to the string ``first``.  A callable is used by a
+directive to defer the result of a user's call to a directive until conflict
+detection has had a chance to do its job.
+
+Other arguments exist to the :meth:`~pyramid.config.Configurator.action`
+method, including ``args``, ``kw``, ``order``, and ``introspectables``.  
+
+``args`` and ``kw`` exist as values, which, if passed, will be used as
+arguments to the ``callable`` function when it is called back.  For example
+our directive might use them like so:
+
+.. code-block:: python
+   :linenos:
+
+   def add_jammyjam(config, jammyjam):
+       def register(*arg, **kw):
+           config.registry.jammyjam_args = arg
+           config.registry.jammyjam_kw = kw
+           config.registry.jammyjam = jammyjam
+       config.action('jammyjam', register, args=('one',), kw={'two':'two'})
+
+In the above example, when this directive is used to generate an action, and
+that action is committed, ``config.registry.jammyjam_args`` will be set to
+``('one',)`` and ``config.registry.jammyjam_kw`` will be set to
+``{'two':'two'}``.  ``args`` and ``kw`` are honestly not very useful when
+your ``callable`` is a closure function, because you already usually have
+access to every local in the directive without needing them to be passed
+back.  They can be useful, however, if you don't use a closure as a callable.
+
+``order`` is a crude order control mechanism.  ``order`` defaults to the
+integer ``0``; it can be set to any other integer.  All actions that share an
+order will be called before other actions that share a higher order.  This
+makes it possible to write a directive with callable logic that relies on the
+execution of the callable of another directive being done first.  For
+example, Pyramid's :meth:`pyramid.config.Configurator.add_view` directive
+registers an action with a higher order than the
+:meth:`pyramid.config.Configurator.add_route` method.  Due to this, the
+``add_view`` method's callable can assume that, if a ``route_name`` was
+passed to it, that a route by this name was already registered by
+``add_route``, and if such a route has not already been registered, it's a
+configuration error (a view that names a nonexistent route via its
+``route_name`` parameter will never be called).
+
+``introspectables`` is a sequence of :term:`introspectable` objects.  Using
+``introspectables`` allows you to plug into Pyramid's configuration
+introspection system.
+