The surroundings of system calls are illustrated by
<citerefentry>
  <refentrytitle>intro</refentrytitle>
  <manvolnum>2</manvolnum>
</citerefentry>.
A general purpose interface is described by
<citerefentry>
  <refentrytitle>syscall</refentrytitle>
  <manvolnum>2</manvolnum>
</citerefentry>.
I found no man-page listing available system calls; a look into
directory <filename>/usr/share/man/man2</filename> should do.
Anyway, the statement <literal>&xml.magic.revealed.syscall.asm;</literal>
corresponds to the value of <literal>SYS_write</literal> in
<filename>/usr/include/sys/syscall.h</filename>.
