code: func NewDirectoryEntryFromBlobRef(ctx context.Context, fetcher blob.Fetcher, blobRef blob.Ref) (DirectoryEntry, error) {
  	ss := new(superset)
  	err := ss.setFromBlobRef(ctx, fetcher, blobRef)
  	if err != nil {
  		return nil, fmt.Errorf("schema/filereader: can't fill superset: %v", err)
  	}
  	return newDirectoryEntry(fetcher, ss)
  }
docs: // NewDirectoryEntryFromBlobRef takes a BlobRef and returns a
  //  DirectoryEntry if the BlobRef contains a type "file", "directory",
  //  "symlink", "fifo" or "socket".
  // TODO: ""char", "block", probably.  later.