code: func (b *BasicFormatter) Format(d diff.Diff) ([]byte, error) {
  	// calling jsonDiff.Format(d) populates the JSON diff's "Lines" value,
  	// which we use to compute the basic dif
  	_, err := b.jsonDiff.Format(d)
  	if err != nil {
  		return nil, err
  	}
  
  	bd := &BasicDiff{}
  	blocks := bd.Basic(b.jsonDiff.Lines)
  	buf := &bytes.Buffer{}
  
  	err = b.tpl.ExecuteTemplate(buf, "block", blocks)
  	if err != nil {
  		return nil, err
  	}
  	return buf.Bytes(), nil
  }
docs: // Format takes the diff of two JSON documents, and returns the difference
  // between them summarized in an HTML document.