Custom restrictions are specific vehicle properties.
Background
Custom restrictions are useful in situations where you need more granular fitment than the vehicle definition. This allows very accurate fitment without relying on unstructured notes.
You will be able to utilize custom restrictions fully when building a customised storefront, for example building an "additional properties required" dropdown on the product or collection page. You can also publish custom restrictions to eBay as Year Restrictions and notes
How to add year restrictions
You will be able to add further year restrictions to the vehicles you've selected. For example, the vehicle definition selected is a Mazda 3 2009-2014, but your part will only fit 2009-2012.
Select the fitment tab > vehicle > add configuration
Select production year from > production year to
You can also add compatibility to multiple listings that fit the same vehicle by selecting the checkbox, and "Add fitment".
How to add other base properties
Similarly, you can follow the steps above, selecting the Base Property needed. These properties will be published to eBay as notes.