@Override
  protected boolean isAvailable(@Nullable PsiElement element, @NotNull Editor editor, @NotNull PsiFile file) {
    PossiblePrefixReference ref = getReference(file, editor);
    return ref != null && ref.resolve() instanceof SchemaPrefix;
  }
@Override
  protected boolean isAvailable(@Nullable PsiElement element, @NotNull Editor editor, @NotNull PsiFile file)