Promise callbacks returning promises

Question

With regard to these great two sources: NZakas - Returning Promises in Promise Chains and MDN Promises, I would like to ask the following:

Each time that we return a

Answer 1

In this example, p2 is a promise. p3 is also a promise originating from p1's fulfillment handler. However p2 !== p3. Instead p2 somehow magically resolves to 43 (how?) and that value is then passed to p3's fulfillment handler. Even the sentence here is confusing.

a simplified version how this works (only pseudocode)

function resolve(value){
    if(isPromise(value)){
        value.then(resolve, reject);
    }else{
        //dispatch the value to the listener
    }
}

the whole thing is quite more complicated since you have to take care, wether the promise has already been resolved and a few more things.