-<literal>addAttribute</literal> is used to add attributes to a message. The
-option value must be of the form <literal>attribute:value</literal> where
-attribute is a numerical value specifying the attribute.
+<literal>addAttribute</literal> is used to add attributes to a
+message. The option value must be on the
+form <literal>attribute:value</literal> where attribute is a numerical
+value specifying the attribute. Simliarly,
+the <literal>addVendorAttribute</literal> is used to specify a vendor
+attribute to be added. The option value must be on the
+form <literal>vendor:subattribute:value</literal>, where vendor and
+subattribute are numerical values.