fast_xs provides C extensions for escaping text. The original String#fast_xs method is based on the xchar code by Sam Ruby: * http://intertwingly.net/stories/2005/09/28/xchar.rb * http://intertwingly.net/blog/2005/09/28/XML-Cleansing _why also packages an older version with Hpricot (patches submitted). The version here should be compatible with the latest version of Hpricot code. Ruby on Rails will automatically use String#fast_xs from either Hpricot or this gem version with the bundled Builder package. String#fast_xs is an almost exact translation of Sam Ruby's original implementation (String#to_xs), but it does escape "&quot;" (which is an optional, but all parsers are able ot handle it. XML::Builder as packaged in Rails 2.0 will be automatically use String#fast_xs instead of String#to_xs available.