Shiki Compatibility

DocTest handles Shiki line highlights and diff markers used in VitePress and similar documentation tools.

What Shiki Adds

VitePress uses Shiki for syntax highlighting and supports special markers in code blocks:

Line Highlights

Curly braces in the fence info string highlight specific lines:

```php{1,4-6}
$a = 1;
$b = 2;
$c = 3;
$d = 4;
$e = 5;
$f = 6;
```

Diff Markers

Comments mark lines as added or removed:

```php
$old = 'before'; 
$new = 'after';  
```

How DocTest Handles Them

DocTest's ShikiFilter processes these markers before executing code:

Line Highlights {1,4-6}

The {...} notation is stripped from the info string so it doesn't interfere with attribute parsing:

```php{1,4-6}  →  ```php

Diff Removal // [!code --]

Lines containing // [!code --] are removed entirely. These represent "old" code that shouldn't execute:

// Before filtering:
$old = 'before'; 
$new = 'after';  

// After filtering:
$new = 'after';

Diff Addition // [!code ++]

The // [!code ++] marker is stripped, but the code is kept:

// Before filtering:
$new = 'after'; 

// After filtering:
$new = 'after';

Practical Example

You can write VitePress documentation with diff markers and DocTest will execute the "after" version:

```php
$greeting = 'Hello';           
$greeting = 'Hello, World!';   
echo $greeting;
```
<!-- doctest: Hello, World! -->

This renders as a nice diff in VitePress while DocTest correctly tests the updated code.

No Configuration Needed

Shiki filtering is always active. It runs automatically during the parsing phase before any execution occurs.