Model
FilterableAttributeList
Magento\Catalog\Model\Layer\Search\FilterableAttributeList
What it does
This class provides a list of product attributes that can be used as filters in the search results page.
It extends the category filterable attribute list but specifically configures attributes to show only those marked as 'filterable in search' rather than in catalog navigation.
Developers use this when customizing layered navigation filters on search result pages.