@Nullable
  private String verifyInnerClassDestination() {
    PsiClass targetClass = findTargetClass();
    if (targetClass == null) return null;

    for (PsiElement element : myElementsToMove) {
      if (PsiTreeUtil.isAncestor(element, targetClass, false)) {
        return RefactoringBundle.message("move.class.to.inner.move.to.self.error");
      }
      final Language targetClassLanguage = targetClass.getLanguage();
      if (!element.getLanguage().equals(targetClassLanguage)) {
        return RefactoringBundle.message(
            "move.to.different.language",
            UsageViewUtil.getType(element),
            ((PsiClass) element).getQualifiedName(),
            targetClass.getQualifiedName());
      }
      if (element.getLanguage().equals(Language.findLanguageByID("Groovy"))) {
        return RefactoringBundle.message("dont.support.inner.classes", "Groovy");
      }
    }

    while (targetClass != null) {
      if (targetClass.getContainingClass() != null
          && !targetClass.hasModifierProperty(PsiModifier.STATIC)) {
        return RefactoringBundle.message("move.class.to.inner.nonstatic.error");
      }
      targetClass = targetClass.getContainingClass();
    }

    return null;
  }
 @Nullable
 private static Pair<PsiElement, TextRange> findExpression(
     PsiElement element, boolean allowMethodCalls) {
   final EditorTextProvider textProvider =
       EditorTextProvider.EP.forLanguage(element.getLanguage());
   if (textProvider != null) {
     return textProvider.findExpression(element, allowMethodCalls);
   }
   return null;
 }
 @Override
 public void visitElement(PsiElement element) {
   if (element.getLanguage() != JavaLanguage.INSTANCE) {
     return;
   }
   if (!PsiUtil.isLanguageLevel5OrHigher(element)) {
     return;
   }
   super.visitElement(element);
 }
  public static String getNewText(PsiElement elt) {
    Project project = elt.getProject();
    PsiFile psiFile = getContainingFile(elt);

    final Document doc = PsiDocumentManager.getInstance(project).getDocument(psiFile);
    if (doc == null) return null;

    final ImplementationTextSelectioner implementationTextSelectioner =
        LanguageImplementationTextSelectioner.INSTANCE.forLanguage(elt.getLanguage());
    int start = implementationTextSelectioner.getTextStartOffset(elt);
    final int end = implementationTextSelectioner.getTextEndOffset(elt);

    final int lineStart = doc.getLineStartOffset(doc.getLineNumber(start));
    final int lineEnd =
        end < doc.getTextLength()
            ? doc.getLineEndOffset(doc.getLineNumber(end))
            : doc.getTextLength();
    return doc.getCharsSequence().subSequence(lineStart, lineEnd).toString();
  }
 public static String getHelpID(PsiElement element) {
   return LanguageFindUsages.INSTANCE.forLanguage(element.getLanguage()).getHelpId(element);
 }