Source Models in Magento 2 and their configuration path

Hi there! Got Magento 2 open in your IDE? Good!
Take a look at the <section id="sales_email">-node in the etc/adminhtml/system.xml of the Sales module. Notice anything… weird? Look at all the source models responsible for rendering e-mail templates. They all use the same source model: Magento\Config\Model\Config\Source\Email\Template.
This might look weird at first. After all: when you look at the configuration, you’ll see that each select-field is only populated with the proper e-mail templates. Like

• New Order (Default)
• New Order for Guest (Default)
• Order Update (Default)
• etc…

“What kind of witchery is this?” you might ask. After all: it’s one and the same source model and it’s not like there is any other parameters sent to the source model through system.xml. Or is there?
Here comes a small trick: look at the source model again. Notice the method getPath() that is called at some point. This is where it gets interesting. The source model in question is extended from Magento\Framework\DataObject. This means that it has the magical getters and setters.
Now look at the method responsible for parsing the <source_model>-node from our system.xml. This method is located at \Magento\Config\Model\Config\Structure\Element\Field::_getOptionsFromSourceModel(). In this method you’ll notice the following line:

Boom! There it is. What the above states means the following:

“If you have a source model in your system.xml, and the source model is a child of Magento\Framework\DataObject, you have knowledge to the path in the configuration from where the source model was invoked.”
In this example this means the following: Looking back at the system.xml-node of the Magento Sales module we can summarize it like this:

This means that in this example the path is sales_email/order/template. In other words: this is the path that getPath() will return in this configuration-node. But in other locations in the XML, the exact same method returns different results.
A small yet handy undocumented feature of Magento 2.