code: @Override
  	public String group() {
  		int i = mAttributes.indexOf(';');
  		return (i < 0) ? mAttributes.trim() : mAttributes.substring(0, i).trim();
  	}
docs: Get the first item (everything before first semicolon, if it has one)
  in the attribute field, which is assumed to
  be a group identifer. This is appropriate for GFF1 files and variants. It is not
  appropriate for GTF and GFF2 files, although they may use a named attribute key,
  such as "gene_id" or "transcript_id", for grouping.
  
  @return The group id. Everything before the first semicolon in the attributes string (minus trailing whitespace).