Function class 

pub fn class(name: &str, opts: &Emit) -> String

A prefixed class name.

Public, for the renderers that emit markup this crate does not. A screen renderer writing class="row" has to prefix it the way the stylesheet half does, or a prefixed app gets rules matching everything except the elements that renderer wrote, and the failure is invisible: the CSS stays valid and one element is unstyled. Call this rather than copying it.