programmatic.md in vagrant-compose-0.7.2

- old
+ new

@@ -300,13 +300,13 @@
 end
 ```
 
 As you can see, `consul` and `docker` ansible_groups now include both nodes from `consul-agent` and `load-balancer` node set; vice versa, other groups like `registrator`, `consul-template`, `nginx` contain node only from one of the two nodes set.
 
-Ansible playbook can leverage on groups for providing machines with the required software stacks.
+Ansible playbook can additionally leverage on groups for providing machines with the required software stacks.
 
-NB. you can see resulting ansible_groups by using `debug` command with `verbose` equal to `true`.
+> NB. you can see resulting ansible_groups by using `debug` command with `verbose` equal to `true`.
 
 ### Defining group vars
 
 In Ansible, the inventory file is usually integrated with a set of variables containing settings that will influence playbooks behaviour for all the host in a group.
 
@@ -327,10 +327,22 @@
   }
   ...
 end
 ```
 
+Additionally, it is possible to set variables for all groups/all hosts, by setting vars for the pre-defined `all` group of groups:
+
+``` ruby
+config.cluster.compose('test') do |c|
+  ...
+  c.ansible_group_vars['all'] = lambda { |context, nodes|
+    return { 'var0' => nodes.length }
+  }
+  ...
+end
+```
+
 Ansible group vars will be stored into yaml files saved into `{cluster.ansible_playbook_path}\group_vars` folder.
 
 The variable  `cluster.ansible_playbook_path` defaults to the current directory  (the directory of the Vagrantfile)  +  `/provisioning`; this value can be changed like any other cluster attributes (see Defining cluster attributes).
 
 ### Defining host vars
@@ -377,10 +389,12 @@
 end
 ```
 
 > Context_vars generator are always executed before group_vars and host_vars generators; the resulting context, is given in input to group_vars and host_vars generators.
 
+> In addition to context vars for groups, it is possible to create context_vars for all groups/all hosts, by setting vars for the pre-defined `all` group of groups; in this case, intuitively, the list of nodes whitin the context contains all the nodes.
+
 Then, you can use the above context var when generating group_vars for nodes in the `consul-agent` group.
 
 ``` ruby
 config.cluster.compose('test') do |c|
   ...
@@ -395,12 +409,10 @@
 ```
 
 ### Group of groups
 A useful ansible inventory feature is [group of groups](http://docs.ansible.com/ansible/intro_inventory.html#hosts-and-groups).
 
-By default vagrant-compose will generate a group named `[all_groups:children]` with all the ansible_groups defined in cluster configuration; however:
-- you cannot rename all_groups
-- you cannot exclude any ansible group from all_groups.
+By default ansible has a group named `[all]` with all the nodes defined in cluster configuration.
 
 If you need higher control on groups of groups you can simply add a new item to the variable `config.cluster.ansible_groups` before creating nodes.
 
 For instance:
 ```ruby