If B<X509_ADD_FLAG_UP_REF> is set then
the reference counts of those certificates added successfully are increased.
-If B<X509_ADD_FLAG_PREPEND> is set then the certifcates are prepended to I<sk>.
+If B<X509_ADD_FLAG_PREPEND> is set then the certificates are prepended to I<sk>.
By default they are appended to I<sk>.
In both cases the original order of the added certificates is preserved.