The double hyphen is actually part of a pretty common naming convention (BEM-style) for distinguishing between separate components, component modifiers, and component sub-objects.

Examples: https://gist.github.com/1309546 http://nicolasgallagher.com/about-html-semantics-front-end-a... http://csswizardry.com/2013/01/mindbemding-getting-your-head... http://engineering.appfolio.com/2012/11/16/css-architecture