=for apidoc av_fetch
Returns the SV at the specified index in the array. The C<key> is the
-index. If C<lval> is set then the fetch will be part of a store. Check
-that the return value is non-null before dereferencing it to a C<SV*>.
+index. If lval is true, you are guaranteed to get a real SV back (in case
+it wasn't real before), which you can then modify. Check that the return
+value is non-null before dereferencing it to a C<SV*>.
See L<perlguts/"Understanding the Magic of Tied Hashes and Arrays"> for
more information on how to use this function on tied arrays.
+The rough perl equivalent is C<$myarray[$idx]>.
=cut
*/
This relies on the fact that uninitialized array elements are set to
C<&PL_sv_undef>.
+Perl equivalent: C<exists($myarray[$key])>.
+
=cut
*/
bool