In a recent discussion, my counterpart was of the opinion that "you" in the PHB applies only to player characters. The argument was that since it is the "Player's Handbook", the rules address specifically the players, so when they say "you" these rules apply to the players, but not other creatures.
I tried to explain the rules in the PHB apply to everyone, PCs, NPCs, monsters alike. It is clear to me that they must apply to other creatures too, because there otherwise would be no rules for those. There is no separate rules section for them in the DMG or MM.
But, unfortunately, when looking for a statement about whom "you" refers to, and checking the front matter and introductory pages of the PHB to support this, I could find no such explanation.
Is there any textual support about whom "you" refers to?