Sentence:  Now bands like Mumford and the Lumineers are fulfilling that role, but they're also becoming the latest <WSD>installment</WSD> of the whole "indie goes mainstream"/"mainstream co-opt indie" thing that's been happening since Seth Cohen's heyday -- or, you know, since Don Draper married Megan. 
Meaning of the word marked with <WSD> tags:  A part of anything that is performed in parts, spread over time.