documentation update and docstrings

doc/config.txt

@@ -61,6 +61,11 @@ Let's make the protocol of accessing a config's attribute explicit
 4. If an option is declared, and a value has been set, the returned value is
    the value of the option.
 
+But there are special exceptions. We will see later on that an option can be a 
+:term:`mandatory option`. A mandatory option is an option that must have a defined value. 
+If no value have been set yet, the value is `None`. 
+When the option is called to retrieve a value, an exception is raised. 
+
 What if a value has been set and `None` is to be returned again ? Don't
 worry, an option value can be "reseted" with the help of the `option.Option.reset()`
 method.
@@ -130,3 +135,9 @@ Here are the (useful) methods on ``Config`` (or `SubConfig`).
     .. rubric:: Methods
 
  
+A :class:`~config.CommonConfig` is a abstract base class. A 
+:class:`~config.SubConfig` is an just in time created objects that wraps an 
+::class:`~option.OptionDescription`. A SubConfig differs from a Config in the 
+::fact that a config is a root object and has an environnement, a context wich 
+::defines the different properties, access rules, vs... There is generally only 
+::one Config, and many SubConfigs.

doc/consistency.txt

@@ -30,6 +30,19 @@ of the same type.
 For example, an :class:`option.IntOption` validator waits for an `int` object of 
 course, an :class:`option.StrOption` validator waits for an `str`, vs...
 
+
+Where are located the values
+-------------------------------
+
+The entry point of the acces to the values is the :class:`setting.Setting()` of 
+the root configuration object, but the values are actually located in the 
+:class:`value.Values()` object, in order to be delegated in some kind of a 
+`tiramisu.storage`, which can be a in-memory storage, or a persistent (for the 
+time being, a sqlite3) storage.
+
+:class:`value.Values()` is also responsible of the owners and the calculation 
+of the options that have callbacks.
+
 Requirements
 ------------
 
@@ -76,3 +89,15 @@ modified at the first calculation.
 .. automodule:: tiramisu.autolib
     :members:
 
+This is the typically protocol for accessing a option's for a calculated value, 
+but some twisted ways are also possible, take a look at the `force_store_value` 
+attribute.
+
+.. glossary:: 
+
+    force store value 
+
+        A calculated value (that is, an option that has a callback) with the 
+        attribute `force_store_value` enabled is considered to be modified at 
+        the first calculation
+