class Regexp::Syntax::Base

def excludes(type, tokens)
  if tokens
    tokens = [tokens] unless tokens.is_a?(Array)
  end
  if @implements[type]
    if tokens
      @implements[type] = @implements[type] - tokens
      @implements[type] = nil if @implements[type].empty?
    else
      @implements[type] = nil
    end
  end
end