code: function prefixClasses(prefix, block){
    utils.assertString(prefix, 'prefix');
    utils.assertType(block, 'block', 'block');
  
    var _prefix = this.prefix;
  
    this.options.prefix = this.prefix = prefix.string;
    block = this.visit(block);
    this.options.prefix = this.prefix = _prefix;
    return block;
  }
docs: Prefix css classes in a block
  
  @param {String} prefix
  @param {Block} block
  @return {Block}
  @api private