Function relative_base 

pub fn relative_base(
    current_path: &[String],
    row_keys: &[usize],
    levels_up: usize,
) -> Vec<String>

The path that a relative path with levels_up further dots starts from: the current field is one level and each further dot moves one more level up, and a row key leaves together with the name of its collection (expressions.md, “Evaluation”).