--- a/docs/ccguide/intercept.refentry	Fri Nov 15 21:49:51 2002 +0000
+++ b/docs/ccguide/intercept.refentry	Fri Nov 15 21:49:51 2002 +0000
@@ -23,7 +23,61 @@
 
 <refsect1><title>Description</title>
 <para>
-Placeholder
+Intercept instructs OS-9 to pass control to the function "func"
+when an interrupt (signal) is received by the current process.
+</para>
+<para>
+If the interrupt processing function has an argument, it will
+contain the value of the signal received. On return from
+"func", the process resumes at the point in the program where
+it was interrupted by the signal. "Interrupt()" is an
+alternative to the use of "signal()" to process interrupts.
+</para>
+<para>
+As an example, suppose we wish to ensure that a partially
+completed output file is deleted if an interrupt is received.
+The body of the program might include:
+<programlisting>
+char *temp_file = "temp"; /* name of temporary file */
+int pn=0;                 /* path number */
+int intrupt();            /* predeclaration */
+
+...
+
+intercept(intrupt);       /* route interrupt processing */
+pn = creat(temp_file,3);  /* make a new file */
+
+...
+
+write(pn,string,count);   /* write string to temp file */
+
+...
+
+close(pn);
+pn=0;
+
+...
+</programlisting>
+The interrupt routine might be coded:
+<programlisting>
+intrupt(sig);
+{
+     if (pn){ /* only done if pn refers to an open file */
+          close(pn);
+          unlink(temp_file); /* delete */
+     }
+exit(sig);
+}
+</programlisting>
+</para>
+</refsect1>
+
+<refsect1><title>Caveats</title>
+<para>
+"Intercept()" and "signal()" are mutually incompatible so that
+calls to both must not appear in the same program. The linker
+guards against this by giving an "entry name clash - _sigint"
+error if it is attempted.
 </para>
 </refsect1>