If a user function needs to print output, it must use one of the
following functions. The normal C functions that print to
stdout such as printf(), puts(), etc. must
not be used, as they will interfere with normal output and will not
be redirected to <EXEC> or <CAPTURE> as needed. These
functions do not automatically HTML-escape their output; the %H
format code must explicitly be used with VXpf() for escapement.
VXpf(const char *fmt, ...)
Replacement for printf(); has the same syntax. Also
understands the same extended codes that <fmt> does.VXwrite(const char *buf, size_t len)
Prints len bytes of buf to the current output. Binary
data is permitted.