code: func (p *pathTree) visitIntermediatesBF(cb func(string) bool) {
  	if p == nil {
  		return
  	}
  	nodes := p.nodes.ToSlice()
  	sort.Strings(nodes)
  	for _, path := range nodes {
  		if !cb(path) {
  			return
  		}
  	}
  }
docs: // visitIntermediatesBF calls cb() for all non-leaf nodes in the tree in
  // breadth-first order (i.e. smallest paths come first).
  //
  // On case-insensitive file systems, all visited nodes are in lowercase,
  // regardless in what case they were added to the tree.
  //
  // nil pathTree is considered empty.