[RPG] Does this errata allow vision out of an area of Darkness

I see nothing there that implies it is a barrier to vision, just an active and utter absence of illumination.

You are quite right - there is nothing in the spell that says it blocks vision, just that the area is in Darkness.

However, a strict reading of normal darkness means you can't see through that (PHB p.183):

Darkness creates a heavily obscured area. Characters face darkness outdoors at night (even most moonlit nights), within the confines of an unlit dungeon or a subterranean vault, or in an area of magical darkness.

And a Heavily Obscured area is (PHB p.183):

A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition (see appendix A).

Which has been erratad as:

A heavily obscured area doesn’t blind you, but you are effectively blinded when you try to see something obscured by it.

So, darkness (magical or otherwise) creates a heavily obscured area. A heavily obscured area "blocks vision entirely".

Now, while it is clear what this means for "opaque fog, or dense foliage" is simple and straightforward - you can't see into this stuff and you can't see through it to stuff on the other side of it.

Applying this to darkness, however, seems to result in nonsense because, in the real world, darkness isn't a thing. In the real world darkness is the absence of light hitting your eyes from a certain direction. This can be because of an actual absence of light (underground) or because, even though the region is full of light none of it is coming your way (space). But this isn't the real world, is it?

So you have 3 options:

1. Darkness works just like it says in the book - you cannot see into it or through it. This would be really cool for a gothic horror campaign even though it would make navigating at night ridiculously hard.
2. Darkness (magical or not) works as it does in the real world - you can't see into it but you can see through it to illuminated areas beyond. I think this is what the rules intended even though they and the errata were poorly drafted.
3. Normal darkness works like 2. Magical darkness works like 1. There is no support for this in the Darkness spell description but this is how it worked in prior editions.

Its your world - make it fun.

Not quite as invisibility since it has its own caveats, emphasis mine.

You are also adept at evading creatures that rely on darkvision. Such creatures gain no benefit when attempting to detect you in dark and dim conditions. Additionally, when the DM determines if you can hide from a creature, that creature gains no benefit from its darkvision. UA: The ranger, revised P. 8

The main difference is that, invisibility does not end when you are detected by other means that are not magical or with special senses but, in the ranger case, the condition/ability ends as soon as the ranger is detected.

The invisibility condition in PHB 191.
An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature’s location can be detected by any noise it makes or any tracks it leaves.

Attack rolls against the creature have disadvantage, and the creature’s attack rolls have advantage.

Now, about detection; attacking or casting a spell make you lose the benefit as stated in PHB. 195. Also, there is a big difference between dark and dim conditions (PHB. 183). The main difference is that with normal sight you can see the ranger in dim conditions but you are blinded in dark conditions. Therefore, the ranger in dim condition is not treated as if it has invisibility/heavily obscured, the ranger is treated as if in dim condition.

(PHB 195) If you are hidden—both unseen and unheard—when you make an attack, you give away your location when the attack hits or misses.

(PHB 183) A given area might be lightly or heavily obscured. In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.
A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition.

Thus, against the ranger when trying to detect him in dark or dim light condition, a Dark Elf and a Human are not treated differently, as if they have the same visual capacities.

As an example, by courtesy of Keithcurtis; Robbie the Ranger and Frank the Fighter are trying to sneak past Danny the Drow and Harry the Human in a dimly lit cavern. Harry has disadvantage on the opposing perception on both the sneakers, while Danny only has disadvantage against Robbie the Ranger.