code: func (as *Step) SetNestLevel(l int) bool {
  	if as.level == l {
  		return false
  	}
  	as.level = l
  
  	// Attach this step to the correct parent step based on nest level. Ascend
  	// up the previously-declared steps.
  	var nestParent *Step
  	for prev := as.prevStep; prev != nil; prev = prev.prevStep {
  		if prev.level < l {
  			nestParent = prev
  			break
  		}
  	}
  	if nestParent == nil || nestParent == as.parent {
  		return true
  	}
  	nestParent.appendSubstep(as)
  	return true
  }
docs: // SetNestLevel sets the nest level of this Step, and identifies its nesting
  // parent.
  //
  // If no parent could be found at level "l-1", the root step will become the
  // parent.