OptionalindexInsert as a new stage at this 0-based stage slot. Overrides target/position.
OptionalpositionInsert before or after the stage holding target.
The custom processor to inject into the pipeline.
OptionaltargetProcessor ID whose stage to insert beside. Use with position.
Per-instance custom processor injection for the engine.
Supports the same positioning as KeyboardEngine.addProcessor:
{ processor, target, position }— insert as a new stage before/after the stage holding a named processor (built-in or custom){ processor, index }— insert as a new stage at a 0-based stage slot{ processor }— append to the end of the chain