- `tagExists` and `clearTags` methods in the Node API
- `addFilter` method in the Node API

About adding filters: rule optimisations that combine rules together make it non-trivial to check whether or not a rule already exists - a rule fused from multiple rules looks very different from the original rule. Checking for existence is therefore only available when optimisations are siwtched off. With optimisations siwtched on, a rule will get added without checking if it already exists

Note the outer-most `Engine` and corresponding Node APIs fail quietly, with only stderr logging in case of errors with existence checking or addition