Nested pre render error

[LitileXueZha]

Here is a demo

Should it be:

//```
// const a = 'b';
//```

Source md:

    ```
    // ```
    // const a = 'b';
    // ```
    ```

[UziTech]

CommonMark demo

The workaround for this is to use more than 3 backticks to start the code block

e.g.

````
//```
// const a = 'b';
//```
````

demo

[LitileXueZha]

ok, thanks

[UziTech]

I'm going to reopen this, since it is still a bug, so we can keep track of the issues