public static boolean isXsltFile(@NotNull PsiFile psiFile) {
    if (psiFile.getFileType() != XmlFileType.INSTANCE) return false;

    if (!(psiFile instanceof XmlFile)) return false;

    final XsltChecker.LanguageLevel level = getXsltLanguageLevel(psiFile);
    return level != XsltChecker.LanguageLevel.NONE;
  }
public static boolean isXsltFile(@NotNull PsiFile psiFile)