# File lib/docbook.rb, line 48
    def self.invalid?(file)
      # Obnoxiously, we can't just check for a non-zero output...
      cmd = %Q(#{CHECKER} "#{file}")
      output = `#{cmd} 2>&1`

      if $?.to_i == 0
        return false
      else  
        STDERR.puts output if $DEBUG
        return output
      end  
    end