public static boolean isXslOrXsltFile(@Nullable PsiFile file) {
    return file != null && file.getFileType() == XmlFileType.INSTANCE
        && (FileUtilRt.extensionEquals(file.getName(), "xsl") || FileUtilRt.extensionEquals(file.getName(), "xslt"));
  }
public static boolean isXslOrXsltFile(@Nullable PsiFile file)