code: boolean containsRule( Rule rule ) {
          for( int i = state.stackIdx - 1; i >= 0; i-- ) {
              if( rule == state.stack.get( i ).mixin ) {
                  return true;
              }
          }
          return false;
      }
docs: A mixin inline never it self.
  
  @param rule the rule
  @return true, if the mixin is currently formatting