code: func NSFindOneChildCtx(ctx NSContext, el *etree.Element, namespace, tag string) (*etree.Element, error) {
  	var found *etree.Element
  
  	err := NSFindChildrenIterateCtx(ctx, el, namespace, tag, func(ctx NSContext, el *etree.Element) error {
  		found = el
  		return ErrTraversalHalted
  	})
  
  	if err != nil && err != ErrTraversalHalted {
  		return nil, err
  	}
  
  	return found, nil
  }
docs: // NSFindOneCtx conducts a depth-first search for the specified element. If such an
  // element is found a reference to it is returned.