code: func focusedSample(s *Sample, focus, ignore TagMatch) (fm, im bool) {
  	fm = focus == nil
  	for key, vals := range s.Label {
  		for _, val := range vals {
  			if ignore != nil && ignore(key, val, 0) {
  				im = true
  			}
  			if !fm && focus(key, val, 0) {
  				fm = true
  			}
  		}
  	}
  	for key, vals := range s.NumLabel {
  		for _, val := range vals {
  			if ignore != nil && ignore(key, "", val) {
  				im = true
  			}
  			if !fm && focus(key, "", val) {
  				fm = true
  			}
  		}
  	}
  	return fm, im
  }
docs: // focusedTag checks a sample against focus and ignore regexps.
  // Returns whether the focus/ignore regexps match any tags