vscode markdown代码片段 无法提示

最近遇到一个问题，用 Vscode 写代码有提示，为什么写 markdown文档没有呢，很不方便。

方法

添加markdomw代码片段

Code-首选项-用户代码片段 输入 markdown，编辑 markdown.json：

{
    // Place your snippets for markdown here. Each snippet is defined under a snippet name and has a prefix, body and 
    // description. The prefix is what is used to trigger the snippet and the body will be expanded and inserted. Possible variables are:
    // $1, $2 for tab stops, $0 for the final cursor position, and ${1:label}, ${2:another} for placeholders. Placeholders with the 
    // same ids are connected.
    // Example:
    // "Print to console": {
    //  "prefix": "log",
    //  "body": [
    //      "console.log('$1');",
    //      "$2"
    //  ],
    //  "description": "Log output to console"
    // }

    "markdwon php": {
        "prefix": "php",
        "body": [
            "```php",
            "$1",
            "```"            
        ],
        "description": "输出php代码块"
    },
}

修改setting.json文件

添加好了代码片段之后，到.md文件，输入php，发现没有提示。
按快捷键：command+shift+ p，输入 setting.json enter
打开 setting.json,添加一段：

"[markdown]":  {
    "editor.quickSuggestions": true
  }

然后在到md文件中，输入 php ，就有提示了