Sigh, I've been bitten by this at least 3-4 times. First a couple of years ago with some version of YAML. And then with some version of YAML::Parser::Syck. And just now with YAML::Syck. I'm using Perl, Ruby, PHP, and to a much less extent Python. Strangely, all of them but Perl have had no problem with No being false, but interestingly in Perl we are confused every now and then and load No as the string 'No'. What's going on here? :-)