message: refactor: update comments and internal names a bit
diff: @@ -128,12 +128,23 @@ export class SafeSubscriber<T> extends Subscriber<T> {
  complete?: (() => void) | null
  ) {
  super();
  +
  + // If we don't have arguments, or the observer passed is already EMPTY_OBSERVER,
  + // use EMPTY_OBSERVER. This is just to save a little on object allocations.
  this.destination = EMPTY_OBSERVER;
  if ((observerOrNext || error || complete) && observerOrNext !== EMPTY_OBSERVER) {
  + // We've got either functions or an observer to deal with
  + // let's figure that out here.
  +
  let next: ((value: T) => void) | undefined;
  if (isFunction(observerOrNext)) {
  next = observerOrNext;
  } else if (observerOrNext) {
  + // Even if it's an observer, we have to pull the handlers off and
  + // capture the owner object as the context. That is because we're
  + // going to put them all in a new destination with ensured methods
  + // for `next`, `error`, and `complete`. That's part of what makes this
  + // the "Safe" Subscriber.
  ({ next, error, complete } = observerOrNext);
  let context: any;
  if (this && config.useDeprecatedNextContext) {
  @@ -150,16 +161,25 @@ export class SafeSubscriber<T> extends Subscriber<T> {
  complete = complete?.bind(context);
  }
  + // Once we set the destination, the superclass `Subscriber` will
  + // do it's magic in the `_next`, `_error`, and `_complete` methods.
  this.destination = {
  next: next || noop,
  - error: error || handleError,
  + error: error || defaultErrorHandler,
  complete: complete || noop,
  };
  }
  }
  }
  -function handleError(err: any) {
  +/**
  + * An error handler used when no error handler was supplied
  + * to the SafeSubscriber -- meaning no error handler was supplied
  + * do the `subscribe` call on our observable.
  + * @param err The error to handle
  + */
  +function defaultErrorHandler(err: any) {
  + // TODO: Remove in v8.
  if (config.useDeprecatedSynchronousErrorHandling) {
  throw err;
  }
  @@ -174,6 +194,6 @@ function handleError(err: any) {
  export const EMPTY_OBSERVER: Readonly<Observer<any>> = {
  closed: true,
  next: noop,
  - error: handleError,
  + error: defaultErrorHandler,
  complete: noop,
  };
  