Defining the zip attributes based on the xsd schema

guides/v2.1/howdoi/checkout/checkout_zip.md

@@ -17,6 +17,34 @@ When a shopper specifies the country and ZIP code in the shipping address during
 In Magento the input masks for the **ZIP code** field are specified in the `<Magento_Directory_module_dir>/etc/zip_codes.xml`. Input masks are specified per country, and are entered in the form of regular expressions.
 The syntax of defined by the [zip_code.xsd]({{ site.mage2bloburl }}/{{ page.guide_version }}/app/code/Magento/Directory/etc/zip_codes.xsd) scheme.
 
+The following table defines the `zip` node attributes:
+
+ Attribute name | Required | Description
+--- | --- | ---
+`countryCode` | Yes | The country code (Alpha-2 format) for which the zip is defined
+
+```xml
+    <zip countryCode="US">
+        <!-- Here we add the zip codes -->
+    </zip>
+```
+
+The following table defines the `code` node attributes:
+
+ Attribute name | Required | Description
+--- | --- | ---
+`id` | Yes | A random unique name within the same list.
+`example` | Yes | An example of the allowed pattern.
+`active` | No | Defines if this zip pattern is active or not.
+
+You can define several zip `code` patterns for the same country, by passing a list of `codes`.
+```xml
+    <codes>
+        <code id="pattern_1" active="true" example="12345">^[0-9]{5}$</code>
+        <code id="pattern_2" active="true" example="AB1234">^[a-zA-z]{2}[0-9]{4}$</code>
+    </codes>
+```
+
 For the sake of compatibility, upgradability, and easy maintenance, do not edit the default Magento code. Add your customizations in a separate, custom module. For your ZIP code input mask customization to be applied correctly, your custom module should depend on the `Magento_Directory` module. Do not use `Ui` for your custom module name, because `%Vendor%_Ui` notation, required when specifying paths, might cause issues.
 
 ## Add custom ZIP code input masks {#add}