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No smoking marijuana in public. An age limit of 21. An option for home delivery.

And what about all those prior convictions for marijuana-related offenses? Automatically expunged.

Those were some of the recommendations made in a 77-page report from New York City officials for how to approach the legalization of recreational marijuana use, an eventuality that Mayor Bill de Blasio acknowledged earlier this year even as he stopped short of endorsing the move.

Now, three days after Gov. Andrew M. Cuomo declared marijuana legalization a key part of his agenda for the state in 2019, Mr. de Blasio endorsed legalization for the first time — with caveats.

“I have been convinced that we can establish a regulatory framework that keeps our streets safe, rights the wrongs of the past, and gives economic opportunity to communities hit hardest by the war on drugs,” Mr. de Blasio said in a statement to The New York Times on Wednesday. He is expected to discuss the report, a copy of which was obtained by The Times, at a news conference on Thursday.