While I was reading the book "Practical English Usage, 3rd edition, page 477, I came across an example, wherein the writer, Michael Swan, of worldwide fame, made a strange claim. Why strange? Because I firmly believe in this very section he's trying to explain things using decontextualized examples.
He says sentence (a) below is wrong:
(a) Suddenly the door opened itself.
Although I believe the above sentence is less common than the version with no reflexive pronoun, I don't think it's grammatically wrong. Well, when prompted, a self-opening door opens itself. Right?
What's more, I am pretty sure the sentence (b) below is perfectly grammatical.
(b) The door opens itself when someone comes near it.
Of course, by "the door" the writer probably means a self-contained unit that includes the door and the opening mechanism. Otherwise, the better version sure is: The door opens when someone comes near it.
That's why I say: Context is important.
I would be happy if you would share your opinions with me.