code: func (x *Exif) LoadTags(d *tiff.Dir, fieldMap map[uint16]FieldName, showMissing bool) {
  	for _, tag := range d.Tags {
  		name := fieldMap[tag.Id]
  		if name == "" {
  			if !showMissing {
  				continue
  			}
  			name = FieldName(fmt.Sprintf("%v%x", UnknownPrefix, tag.Id))
  		}
  		x.main[name] = tag
  	}
  }
docs: // LoadTags loads tags into the available fields from the tiff Directory
  // using the given tagid-fieldname mapping.  Used to load makernote and
  // other meta-data.  If showMissing is true, tags in d that are not in the
  // fieldMap will be loaded with the FieldName UnknownPrefix followed by the
  // tag ID (in hex format).