text: var utils = require('../utils');
  
  /**
   * Prefix css classes in a block
   *
   * @param {String} prefix
   * @param {Block} block
   * @return {Block}
   * @api private
   */
  
  module.exports = 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;
  };
  