Is Indexable Determiner
If an entity is indexable is determined by Klevu\Indexing\Service\Determiner\IsIndexableDeterminer This determiner loops through all injected Klevu\IndexingApi\Service\Determiner\IsIndexableConditionInterface classes. If any of these return false; then the entity is set to not indexable and will not be indexed with Klevu. If they all return true; then the entity is indexable and can be indexed with Klevu.
All entity types module-ms-indexing-categories, module-ms-indexing-cms and module-m2-indexing-products create virtualTypes of this class and inject an array of conditions. e.g. for products the virtualType in di.xml looks like this
You can add conditions to amend the default behaviour. Let's say you only wanted to index products when the attribute color was pink. You’d inject your condition in to the IsIndexableDeterminer via the isIndexableConditions array in your di.xml
Create that class, which must implement the IsIndexableConditionInterface
See Klevu\IndexingProducts\Service\Determiner\DisabledProductsIsIndexableCondition as an example of a determiner condition.