Configuration can come in many different formats. Each supported format has a related Transformer which is responsible for taking the config in its original format and merging it into an instance of ConfigCollectionInterface.
The merged config is an instance of ConfigCollectionInterface which is made up of many ConfigItemInterface's.
As the config collection is passed through transformers, its content is updated with new ConfigItem's containing the value of a given key as well as some meta data about where the key came from. This metadata includes the tranformer which updates the value of the key and where the key came from.
The priority in which transformers are merged is implied by the order in which ->transform() is called on each transformer. The lower priority items are called first and may be overwritten by later transformations.
The data flow is shown below:
+-----------------+
| |
| Config |
| Collection |
| |
+--------+--------+
|
|
v
+-------------------+--------------------+
| |
| Transformer 1 |
| |
+-------------------+--------------------+
|
|
v
+-------------------+--------------------+
| |
| Transformer 2 |
| |
+-------------------+--------------------+
|
|
v
+-------------------+--------------------+
| |
| Transformer 3 |
| |
+-------------------+--------------------+
|
|
v
+--------+--------+
| |
| Config |
| Collection |
| |
+-----------------+