-The system missing value.
-
-@item flt64 highest;
-The value used for HIGHEST in missing values.
-
-@item flt64 lowest;
-The value used for LOWEST in missing values.
+@itemx flt64 highest;
+@itemx flt64 lowest;
+The system missing value, the value used for HIGHEST in missing
+values, and the value used for LOWEST in missing values, respectively.
+@xref{System File Format}, for more information.
+
+The SPSSWriter library in PHP, which identifies itself as @code{FOM
+SPSS 1.0.0} in the file header record @code{prod_name} field, writes
+unexpected values to these fields, but it uses the same values
+consistently throughout the rest of the file.