code: function augmentPrefix(bemNode, prefix) {
  
      assert(typeof prefix === 'string', 'options.prefix must be string');
  
      // `md-` is already prefix, replace it
      if (bemNode.isRoot) {
          bemNode.block = bemNode.block.replace('md-', prefix);
      } else {
          // in other cases just add prefix
          bemNode.block = `${prefix}${bemNode.block}`;
      }
  
      return bemNode;
  }
docs: Add prefix to all block names
  *Important*: in root block prefix `md-` will be replaced.
  
  @param {Object} bemNode - representation of bem entity
  @param {string} prefix - new prefix
  @returns {Object} bemNode