What is the purpose of the first two parameters for the `Emitter` constructor?

[dead-claudia]

The Emitter constructor, as far as I understand based on my reading of this, has three parameters:

• d - The received datum
• i - The implicit metadata
• n - The current context

The third is obvious - it provides the methods that actually make it useful in practice, and it functions similarly to the Observable constructor, just with different names for each of the methods. But the first two to me seem like they aren't even used.