diff --git a/docs.sgml b/docs.sgml
index dfaa580c..2a5356f0 100644
--- a/docs.sgml
+++ b/docs.sgml
@@ -2296,6 +2296,13 @@ OUTPUT:
                         <entry><emphasis>n/a</emphasis></entry>
                         <entry>the equation to execute</entry>
                     </row>
+                    <row>
+                        <entry>format</entry>
+                        <entry>string</entry>
+                        <entry>No</entry>
+                        <entry><emphasis>n/a</emphasis></entry>
+                        <entry>the format of the result (sprintf)</entry>
+                    </row>
                     <row>
                         <entry>var</entry>
                         <entry>numeric</entry>