code: private static boolean isValidStandardOperator(final Element e) {
          if (e.getKind() == ElementKind.FIELD) {
              return e.getModifiers().containsAll(EnumSet.of(Modifier.PUBLIC, Modifier.STATIC, Modifier.FINAL));
          }
          if (e.getKind() == ElementKind.METHOD) {
              return e.getModifiers().containsAll(EnumSet.of(Modifier.PUBLIC, Modifier.STATIC))
                  && ((ExecutableElement) e).getParameters().isEmpty();
          }
          if (e.getKind() == ElementKind.CLASS) {
              if (e.getModifiers().contains(Modifier.ABSTRACT) || findDefaultConstructor((TypeElement) e) == null) {
                  return false;
              }
              Element current = e;
              while (current.getKind() == ElementKind.CLASS) {
                  final TypeElement t = (TypeElement) current;
                  if (t.getNestingKind() == NestingKind.TOP_LEVEL) {
                      return true;
                  }
                  if (t.getNestingKind() == NestingKind.MEMBER && t.getModifiers().contains(Modifier.STATIC)) {
                      current = t.getEnclosingElement();
                      continue;
                  }
                  break;
              }
          }
          return false;
      }
docs: Must be a public static concrete class with a default constructor, public static zero-arg method, or public
  static final field.
  
  @param e
  @return boolean