code: func (p *Profile) ShowFrom(showFrom *regexp.Regexp) (matched bool) {
  	if showFrom == nil {
  		return false
  	}
  	// showFromLocs stores location IDs that matched ShowFrom.
  	showFromLocs := make(map[uint64]bool)
  	// Apply to locations.
  	for _, loc := range p.Location {
  		if filterShowFromLocation(loc, showFrom) {
  			showFromLocs[loc.ID] = true
  			matched = true
  		}
  	}
  	// For all samples, strip locations after the highest matching one.
  	s := make([]*Sample, 0, len(p.Sample))
  	for _, sample := range p.Sample {
  		for i := len(sample.Location) - 1; i >= 0; i-- {
  			if showFromLocs[sample.Location[i].ID] {
  				sample.Location = sample.Location[:i+1]
  				s = append(s, sample)
  				break
  			}
  		}
  	}
  	p.Sample = s
  	return matched
  }
docs: // ShowFrom drops all stack frames above the highest matching frame and returns
  // whether a match was found. If showFrom is nil it returns false and does not
  // modify the profile.
  //
  // Example: consider a sample with frames [A, B, C, B], where A is the root.
  // ShowFrom(nil) returns false and has frames [A, B, C, B].
  // ShowFrom(A) returns true and has frames [A, B, C, B].
  // ShowFrom(B) returns true and has frames [B, C, B].
  // ShowFrom(C) returns true and has frames [C, B].
  // ShowFrom(D) returns false and drops the sample because no frames remain.