Edges are links to the first and last page. Most commonly they are rendered
as normal page links for the 1st page and page with the number of the last
page, as icons, or as links with labels "First"/"Last". You can choose to
hide them by setting hide_edges parameter to
true. If you want to show them, but instead of page numbers
you want to have custom labels, you can set start_label and
end_label parameters to the desired values.