would be longer than 60 characters; otherwise it is padded on the right
with spaces.
+The product name field allow readers to behave differently based on
+quirks in the way that particular software writes system files.
+@xref{Value Labels Records}, for the detail of the quirk that the PSPP
+system file reader tolerates in files written by ReadStat, which has
+@code{https://github.com/WizardMac/ReadStat} in @code{prod_name}.
+
@anchor{layout_code}
@item int32 layout_code;
Normally set to 2, although a few system files have been spotted in
Number of data elements per case. This is the number of variables,
except that long string variables add extra data elements (one for every
8 characters after the first 8). However, string variables do not
-contribute to this value beyond the first 255 bytes. Further, system
-files written by some systems set this value to -1. In general, it is
+contribute to this value beyond the first 255 bytes. Further, some
+software always writes -1 or 0 in this field. In general, it is
unsafe for systems reading system files to rely upon this value.
@item int32 compression;
have value labels, but their value labels are recorded using a
different record type (@pxref{Long String Value Labels Record}).
+ReadStat (@pxref{File Header Record}) writes value labels that label a
+single value more than once. In more detail, it emits value labels
+whose values are longer than string variables' widths, that are
+identical in the actual width of the variable, e.g.@: labels for
+values @code{ABC123} and @code{ABC456} for a string variable with
+width 3. For files written by this software, PSPP ignores such
+labels.
+
The value label record has the following format:
@example
Record type. Always set to 6.
@item int32 n_lines;
-Number of lines of documents present.
+Number of lines of documents present. This should be greater than
+zero, but ReadStats writes system files with zero @code{n_lines}.
@item char lines[][80];
Document lines. The number of elements is defined by @code{n_lines}.
variable @code{bias} from the file header. For example,
code 105 with bias 100.0 (the normal value) indicates a numeric variable
of value 5.
-One file has been seen written by SPSS 14 that contained such a code
-in a @emph{string} field with the value 0 (after the bias is
-subtracted) as a way of encoding null bytes.
+
+A code of 0 (after subtracting the bias) in a string field encodes
+null bytes. This is unusual, since a string field normally encodes
+text data, but it exists in real system files.
@item 252
End of file. This code may or may not appear at the end of the data