func (p *Paragraph) RunAt(pos int) Run {
	c := 0
	runNumber := 0
	for i, r := range p.o.runes {
		c += len(r)
		if pos < c {
			runNumber = i
		}
	}
	return p.o.Run(runNumber)
}

func calculateOrdering(levels []level, runes []rune) Ordering {
	var curDir Direction

	prevDir := Neutral
	prevI := 0

	o := Ordering{}
	// lvl = 0,2,4,...: left to right
	// lvl = 1,3,5,...: right to left