I noticed that MTG has an update to the rules for targeting. I don't know how long ago it was changed (the post containing this rule was from 2015), but there used to be this rule:
114.2 Only permanents are legal targets for spells and abilities, unless a spell or ability (a) specifies that it can target an object in another zone or a player, (b) targets an object that can't exist on the battlefield, such as a spell or ability, or (c) targets a zone.
This rule has now been changed:
115.2. Only permanents are legal targets for spells and abilities, unless a spell or ability (a) specifies that it can target an object in another zone or a player, or (b) targets an object that can’t exist on the battlefield, such as a spell or ability. See also rule 115.4.
Was the "targets a zone" text ever relevant? I am pretty sure that no card currently targets a zone (and if such a card existed, it would be strange to remove that part of the rules). But was there ever an old wording on a card (or just a weird rules situation) where a zone would be targeted?
Note that "target player's library" or "target player's hand" targets the player, not the zone (at least under the current rules).