When entering copy mode in tmux, an indicator in the upper right corner shows "[0/0]". I can't find any documentation in the man page about what these numbers mean, and it's difficult to search since Google throws away the brackets and slash.
This is generated by window_copy_write_line() in window-copy.c:
if (py == 0) {
size = xsnprintf(hdr, sizeof hdr,
"[%u/%u]", data->oy, screen_hsize(data->backing));
if (size > screen_size_x(s))
size = screen_size_x(s);
screen_write_cursormove(ctx, screen_size_x(s) - size, 0);
screen_write_puts(ctx, &gc, "%s", hdr);
but the variable names aren't very instructive to someone who isn't familiar with the code.
Any hints as to what these numbers mean?