How should the "and/or" text of a card be interpreted?

Question

How should the "and/or" text of a card be interpreted? For example on a card like Nahiri's Wrath the text reads:

Nahiri's Wrath deals damage equal to the total converted mana cost of the discarded cards to each of up to X target creatures and/or planeswalkers.

For the remainder of this question, let's fix X at 2 to keep things simple.

Should the "and/or" be interpreted such that the effect is applied to a combination of targets the player chooses. That is to say for Nahiri's Wrath the player could perform one of the following options:

1. Nahiri's Wrath deals damage to each of two target creatures.
2. Nahiri's Wrath deals damage to each of two target planeswalkers.
3. Nahiri's Wrath deals damage to each of one target creature and one target planeswalker.

Or should the card's effect be expanded and applied to both sides of the "and/or". With this interpretation the player would have to the following two options when playing Nahiri's Wrath:

1. Nahiri's Wrath deals damage to each of X target creatures and Nahiri's Wrath deals damage to each of X target planeswalkers
2. Nahiri's Wrath deals damage to each of X target creatures or Nahiri's Wrath deals damage to each of X target planeswalkers

The confusion stems from comments on the Pinnacle of Rage's discussion page (which was formerly formerly worded using the same phrasing) where some commenters have said things like:

So this lets you do a total of 12 damage? 3 each to 2 target creatures AND 3 each to 2 target players, one of which could be a planeswalker? That's how the "and/or" works, right? You can choose. Otherwise it would just be "or"...

Answer 1

You must choose X different^[1] targets, and the targets can be creatures and/or planeswalkers. With X=2,

1. You can target two different creatures,
2. You can target two different planeswalkers, or
3. You can target a creature and a different permanent that's a planeswalker.

This is confirmed by a ruling for Pinnacle of Rage: "You must choose two legal targets to cast Pinnacle of Rage." (The ruling dates back to when Pinnacle of Rage still used the same wording about which you are asking.)

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Notes:

1. 114.3. The same target can’t be chosen multiple times for any one instance of the word “target” on a spell or ability. [...]