@Override
  public PsiReference @NotNull [] getReferencesByElement(@NotNull PsiElement element, @NotNull ProcessingContext context) {
    return element instanceof XmlAttributeValue ?
           MicrodataUtil.getUrlReferencesForAttributeValue((XmlAttributeValue)element) :
           PsiReference.EMPTY_ARRAY;
  }
@Override
  public PsiReference @NotNull [] getReferencesByElement(@NotNull PsiElement element, @NotNull ProcessingContext context)