Listening changes in parents to update custom variant fields.

Hello,

I have created extension methods on my variant content like ProductDescription, ProductStyle, and ProductSubStyle. The values come from the parent product. If I update a variant item, their custom properties are indexed correctly in Epifind, but if I update their products (e.g. ProductDescription field), the custom field in the variants is not updated. How can I include the variant dependencies of products when indexing?