code: func (p *Profile) FilterSamplesByTag(focus, ignore TagMatch) (fm, im bool) {
  	samples := make([]*Sample, 0, len(p.Sample))
  	for _, s := range p.Sample {
  		focused, ignored := true, false
  		if focus != nil {
  			focused = focus(s)
  		}
  		if ignore != nil {
  			ignored = ignore(s)
  		}
  		fm = fm || focused
  		im = im || ignored
  		if focused && !ignored {
  			samples = append(samples, s)
  		}
  	}
  	p.Sample = samples
  	return
  }
docs: // FilterSamplesByTag removes all samples from the profile, except
  // those that match focus and do not match the ignore regular
  // expression.