Focus Features is in advanced negotations to acquire worldwide rights to “Street Gang,” Marilyn Agrelo’s documentary exploring the “Sesame Street” phenomenon. HBO has acquired U.S. streaming and broadcast rights, Variety has learned.

Introduced to buyers at the AFM by the Exchange, “Street Gang” is partly based on Michael Davis’ best-selling book of the same name published in 2008. It charts the creation of the groundbreaking puppet series which will celebrate its 50th anniversary next year and has become a cultural and social phenomenon.

“Street Gang” sheds light on the most experimental period of the children’s show, and features behind-the-scene footage, as well as interviews with co-creators Joan Ganz Cooney and Lloyd Morrisett, original head writer Norman Stiles, as well as some original cast members and puppeteers including Big Bird puppeteer Caroll Spinney and Prairie Dawn puppeteer Fran Brill.

“Street Gang” is being by produced by Macrocosm Entertainment and Citizen Skull Productions. Producers are Trevor Crafts, Ellen Scherer Crafts, Mark Myers, Lisa Diamond and Heather Kenyon.

Now in production, the documentary has been one of the most buzzed-about titles being sold at the AFM.

It’s been quite a year for documentaries about cherished children’s TV shows: Mr. Rogers documentary “Won’t You Be My Neighbor” has grossed a healthy $22.6 million in the U.S.