+=item B<PerlIO_exportFILE(f,mode)>
+
+Given a PerlIO * create a 'native' FILE * suitable for passing to code
+expecting to be compiled and linked with ANSI C I<stdio.h>. The mode
+argument should be a string as would be passed to fopen/PerlIO_open.
+If it is NULL then - for legacy support - the FILE * is opened in same
+mode as the PerlIO *.
+
+The fact that such a FILE * has been 'exported' is recorded, (normally
+by pushing a new :stdio "layer" onto the PerlIO *), which may affect
+future PerlIO operations on the original PerlIO *. You should not
+call C<fclose()> on the file unless you call C<PerlIO_releaseFILE()>
+to disassociate it from the PerlIO *. (Do not use PerlIO_importFILE()
+for doing the disassociation.)