private void visitOuterLanguageElement(@NotNull final PsiElement element) {
      myHolder.registerOuterLanguageElement(element);
      PsiReference[] references = element.getReferences();
      for (PsiReference reference : references) {
        if (reference instanceof PossiblePrefixReference && ((PossiblePrefixReference)reference).isPrefixReference()) {
          PsiElement resolve = reference.resolve();
          if (resolve instanceof SchemaPrefix) {
            myHolder.addUsedPrefix(((SchemaPrefix)resolve).getName());
          }
        }
      }
    }
private void visitOuterLanguageElement(@NotNull final PsiElement element)