# File lib/html5/filters/validator.rb, line 581
  def check_browsing_context(token, tag_name, attr_name, attr_value)
    return if not attr_value
    return if attr_value[0] != ?_
    attr_value.downcase!
    return if ['_self', '_parent', '_top', '_blank'].include?(attr_value)
    yield({:type => "ParseError",
         :data => "invalid-browsing-context",
         :datavars => {"tagName" => tag_name,
              "attributeName" => attr_name}})
  end