Letter -- contains features to describe a single letter

  use Letter; # a sample derived class from Lingua::FeatureMatrix
  my $matrix = Lingua::FeatureMatrix->new(file => 'lettermatrix.dat',
                                          eme => 'Letter');

  $matrix->matchesFeatureClass('d', 'RISER'); # true
  $matrix->matchesFeatureClass('l', 'FULLWIDTH'); # false

Long and tortured.