texture.sampler auto filtering

The documentation says:

> 5.29.1. texture.sampler
> The index of the sampler used by this texture. When undefined, a sampler with repeat wrapping and auto filtering SHOULD be used.
>
> Type: integer
>
> Required: No
>
> Minimum: >= 0

`repeat wrapping` is obvious, but what does `auto filtering` mean? The filtering options are:

```
9728 NEAREST

9729 LINEAR

9984 NEAREST_MIPMAP_NEAREST

9985 LINEAR_MIPMAP_NEAREST

9986 NEAREST_MIPMAP_LINEAR

9987 LINEAR_MIPMAP_LINEAR
```

The phrase "auto filtering" is used 4 times without explanation in the spec.