=head1 DESCRIPTION
These functions are used to obtain temporary B<BIGNUM> variables from
-a B<BN_CTX> in order to save the overhead of repeatedly creating and
+a B<BN_CTX> (which can been created by using L<BN_CTX_new(3)|BN_CTX_new(3)>)
+in order to save the overhead of repeatedly creating and
freeing B<BIGNUM>s in functions that are called from inside a loop.
A function must call BN_CTX_start() first. Then, BN_CTX_get() may be
BN_CTX_get() returns a pointer to the B<BIGNUM>, or B<NULL> on error.
Once BN_CTX_get() has failed, the subsequent calls will return B<NULL>
as well, so it is sufficient to check the return value of the last
-BN_CTX_get() call.
+BN_CTX_get() call. In case of an error, an error code is set, which
+can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
+
=head1 SEE ALSO