使用这样的代码:varremarkAbstract=require("remark");varremark=remarkAbstract();letremark=remarkAbstract();varast=remark.process(input);但它返回的输出如下:AssertionError:VFile{contents:'#header\n\n20December2012\n\n\n\ncontent1\n\ncontent2\n\n##header2\n',messages:=我想获得AST树likethis