code: func (t *Tar) IncludeRegexp(re *regexp.Regexp, dirOnly bool) {
  	t.ignorePaths = append(t.ignorePaths, ignoreInfo{regexp: re, exclude: false, dirOnly: dirOnly})
  }
docs: // IncludeRegexp adds a Regexp into the list to consider when selectiong files
  // to exclude. Files or directories matching the regexp will _not_ be excluded,
  // even if they matched a previous Regexp. Files are only considered a match if
  // they match the Regexp and isDir is false.