code: function(comment){
      var ast = [];
      if (!comment.buffer) return;
      if (this.pp) push.apply(ast, this.prettyIndent(1, true));
      push.apply(ast, this.buffer('<!--' + (comment.val || '')));
      push.apply(ast, this.visit(comment.block, comment));
      if (this.pp) push.apply(ast, this.prettyIndent(1, true));
      push.apply(ast, this.buffer('-->'));
      return ast;
    }
docs: Visit a `BlockComment`.
  
  @param {Comment} comment
  @api public