Function at 

pub fn at(
    combine: Option<&Kernel>,
    root: WriteRoot<'_>,
    values: Read<'_>,
    ids: Writes<'_>,
    checked: bool,
    settings: Settings,
    output: &mut Buffer,
) -> Result<(), Error>

Writes to the addresses of ids, replacing or combining with the current items. Invalid positions, including fills, write nothing; repeated positions combine with the earlier result.