In #9618, it was pointed out that IDLE Shell inherits from code.InteractiveConsole, and that #7741 proposes to allow multiple statements there.
In 3.5, this example from msg114561 now gives a SyntaxError, as it should.
>>> x = 3
y = 7
Seven years after opening this, I am more appreciative of 'enter and execute (and recall)' one statement at a time, especially for beginners. Ditto for being able to edit a paste before executing. So I am more inclined to just add the note to the doc (which currently says nothing about executing anyway).
Someone who wants to paste, execute, and recall multiple statements as a block, without having output interleaved, can wrap with 'if 1:'.
>>> if 1:
1+2
3+4
3
7