Document the stack functions that are forgiving
I.e., those that can be called with NULL stack parameter or invalid index.
@@ -229,6 +229,13 @@ A failed search is indicated by a B<-1> return value.
STACK_OF(), DEFINE_STACK_OF(), DEFINE_STACK_OF_CONST(), and
DEFINE_SPECIAL_STACK_OF() are implemented as macros.
+It is not an error to call B<sk_I<TYPE>_num>(), B<sk_I<TYPE>_value>(),
+B<sk_I<TYPE>_free>(), B<sk_I<TYPE>_zero>(), B<sk_I<TYPE>_pop_free>(),
+B<sk_I<TYPE>_delete>(), B<sk_I<TYPE>_delete_ptr>(), B<sk_I<TYPE>_pop>(),
+B<sk_I<TYPE>_shift>(), B<sk_I<TYPE>_find>(), B<sk_I<TYPE>_find_ex>(),
+and B<sk_I<TYPE>_find_all>() on a NULL stack, empty stack, or with
+an invalid index. An error is not raised in these conditions.
+
The underlying utility B<OPENSSL_sk_> API should not be used directly.
It defines these functions: OPENSSL_sk_deep_copy(),
OPENSSL_sk_delete(), OPENSSL_sk_delete_ptr(), OPENSSL_sk_dup(),
