What is the fine-grained topic of the following text: Recently I discovered a three-part documentary filmed in 2010 by the BBC following the English National Ballet as they stage a production of the most famous ballet, Swan Lake, with a Visa-challenged and therefore missing prima ballerina; address injuries and challenging casting choices for a production of Romeo and Juliet; and lastly, speed towards opening night of their biggest moneymaker, The Nutcracker, with a brand-new, incomplete, let alone ready, production. Only return the topic.
Behind-the-scenes challenges of the English National Ballet staging various productions