code: public Iterable<Attribute> getOwnLookupAttributes() {
      List<Attribute> ownLookupAttrs =
          stream(getOwnAllAttributes())
              .filter(attr -> attr.getLookupAttributeIndex() != null)
              .collect(toCollection(ArrayList::new));
      if (ownLookupAttrs.size() > 1) {
        ownLookupAttrs.sort(
            (o1, o2) -> o1.getLookupAttributeIndex() < o2.getLookupAttributeIndex() ? -1 : 1);
      }
      return ownLookupAttrs;
    }
docs: Returns attributes that must be searched in case of xref/mref search
  
  @return lookup attributes