He is saying that the indentation you used for your arguments is weird: It's not a standard 4x multiple indentation, nor is it lined with anything either. He's saying it should look like one of:
```D
ptrdiff_t indexOf(Char)(in Char[] s,
//1 indent deep
    dchar c,
    const size_t startIdx,
    CaseSensitive cs = CaseSensitive.yes) pure
```
```D
ptrdiff_t indexOf(Char)(in Char[] s,
//2 indent deep
        dchar c,
        const size_t startIdx,
        CaseSensitive cs = CaseSensitive.yes) pure
```
```D
ptrdiff_t indexOf(Char)(in Char[] s,
/+aligned+/             dchar c,
                        const size_t startIdx,
                        CaseSensitive cs = CaseSensitive.yes) pure
```
But not:

```D
ptrdiff_t indexOf(Char)(in Char[] s,
//unsure...
                      dchar c,
                      const size_t startIdx,
                      CaseSensitive cs = CaseSensitive.yes) pure
```