Function window 

pub(crate) fn window<T>(
    selector: &Selector,
    list: &[T],
    start: usize,
    end: usize,
    parent: Option<String>,
    options: &ReadOptions<'_>,
    render: &dyn Fn(&T) -> Value,
) -> ReadResult
where
    T: HasId,

Fills a window [start, end) of list with whole units until the budget runs out.