Document setting storage and mail sending

doc/development/implementation/email.rst

@@ -0,0 +1,7 @@
+Sending Email
+=============
+
+As pretix allows event organizers to configure how they want to sent emails to their users in multiple ways.
+Therefore, all emails should be sent throught the following function:
+
+.. autofunction:: pretix.base.services.mail.mail

doc/development/implementation/index.rst

@@ -11,6 +11,8 @@ Contents:
    :maxdepth: 2
 
    models
-   background
    urlconfig
    i18n
+   settings
+   background
+   email

doc/development/implementation/settings.rst

@@ -0,0 +1,52 @@
+Settings storage
+================
+
+pretix is highly configurable and therefore needs to store a lot of per-event and per-organizer settings.
+Those settings are stored in the database and accessed through a ``SettingsProxy`` instance. You can obtain
+such an instance from any event or organizer model instance by just accessing ``event.settings``.
+
+Any setting consists of a key and a value. By default, all settings are strings, but the settings system
+includes serializers for serializing the following types:
+
+* Built-in types: ``int``, ``float``, ``decimal.Decimal``, ``dict``, ``list``, ``bool``
+* ``datetime.date``, ``datetime.datetime``, ``datetime.time``
+* ``LazyI18nString``
+* References to Django ``File`` objects that are already stored in a storage backend
+* References to model instances
+
+In code, we recommend to always use the ``.get()`` method on the settings object to access a value, but for
+convenience in templates you can also access settings values at ``settings[name]`` and ``settings.name``.
+
+.. autoclass:: pretix.base.settings.SettingsProxy
+   :members: get, set, delete, freeze
+
+To avoid naming conflicts, plugins are requested to prefix all settings they use with the name of the plugin
+or something unique, e.g. ``payment.paypal.api_key``. To reduce redundant typing of this prefix, we provide
+another helper class:
+
+.. autoclass:: pretix.base.settings.SettingsSandbox
+
+When implementing e.g. a payment or export provider, you do not event need to create this sandbox yourself,
+you will just be passed a sandbox object with a prefix generated from your provider name.
+
+Forms
+-----
+
+We also provide a base class for forms that allow the modification of settings:
+
+.. autoclass:: pretix.base.forms.SettingsForm
+   :members: save
+
+You can simply use it like this::
+
+   class EventSettingsForm(SettingsForm):
+       show_date_to = forms.BooleanField(
+           label=_("Show event end date"),
+           help_text=_("If disabled, only event's start date will be displayed to the public."),
+           required=False
+       )
+       payment_term_days = forms.IntegerField(
+           label=_('Payment term in days'),
+           help_text=_("The number of days after placing an order the user has to pay to "
+                       "preserve his reservation."),
+       )