Function load_edited 

pub fn load_edited(
    root: &Path,
    options: &LoadOptions,
    overlay: &Overlay,
) -> Result<World, Vec<Diagnostic>>

Loads a source tree as it would be with overlay applied, without writing anything. Overlay files are read under the same limits and budget as files on disk, and a directory that holds one exists. One that the overlay leaves without a file holds none, and is ignored where the layout ignores such a directory (FORMAT.md section 2). An overlay of more entries than maximum_entries is refused before anything is read.

Errors

Returns every diagnostic found, sorted by path and position.