String[] @NotNull [] getKnownCharacterClasses(final @NotNull PsiElement element) {
    final RegExpLanguageHost host = findRegExpHost(element);
    return host != null ? host.getKnownCharacterClasses() : myDefaultProvider.getKnownCharacterClasses();
  }
String[] @NotNull [] getKnownCharacterClasses(final @NotNull PsiElement element)