code: func (as AnnotatedSentence) Leaves() (retVal []int) {
  	for i := range as {
  		if len(as.Children(i)) == 0 {
  			retVal = append(retVal, i)
  		}
  	}
  	return
  }
docs: // Leaves returns the *Annotations which are leaves. If the dependency hasn't been set yet, every single *Annotation is a leaf.