code: public static String validate (ActionSequence seq)
      {
          if (StringUtil.isBlank(seq.name)) {
              return "Missing 'name' definition.";
          }
          if (seq.framesPerSecond == 0) {
              return "Missing 'framesPerSecond' definition.";
          }
          if (seq.orients == null) {
              return "Missing 'orients' definition.";
          }
          return null;
      }
docs: Validates that all necessary fields have been parsed and set in
  this action sequence object and are valid.
  
  @return null if the sequence is valid, a string explaining the
  invalidity if it is not.