HTMLEntities可以做到:
: jmglov@laurana; sudo gem install htmlentities
Successfully installed htmlentities-4.2.4
: jmglov@laurana; irb
irb(main):001:0> require 'htmlentities'
=> []
irb(main):002:0> HTMLEntities.new.decode "¡I'm highly annoyed with character references!"
=> "¡I'm highly annoyed with character references!"