code: func newHelperMethodConditionalComment(ln *line, rslt *result, src *source, parent element, opts *Options) (*helperMethodConditionalComment, error) {
  	switch len(ln.tokens) {
  	case 2:
  		return nil, fmt.Errorf("no comment type is specified [file: %s][line: %d]", ln.fileName(), ln.no)
  	case 3:
  		return nil, fmt.Errorf("no condition is specified [file: %s][line: %d]", ln.fileName(), ln.no)
  	}
  
  	commentType := ln.tokens[2]
  
  	if commentType != commentTypeHidden && commentType != commentTypeRevealed {
  		return nil, fmt.Errorf("the comment type is invalid [file: %s][line: %d]", ln.fileName(), ln.no)
  	}
  
  	e := &helperMethodConditionalComment{
  		elementBase: newElementBase(ln, rslt, src, parent, opts),
  		commentType: commentType,
  		condition:   strings.Join(ln.tokens[3:], space),
  	}
  
  	return e, nil
  }
docs: // newHelperMethodConditionalComment creates and returns an HTML comment.