+This record, if present, specifies value labels for long string
+variables.
+
+@example
+/* @r{Header.} */
+int32 rec_type;
+int32 subtype;
+int32 size;
+int32 count;
+
+/* @r{Repeated up to exactly @code{count} bytes.} */
+int32 var_name_len;
+char var_name[];
+int32 var_width;
+int32 n_labels;
+long_string_label labels[];
+@end example
+
+@table @code
+@item int32 rec_type;
+Record type. Always set to 7.
+
+@item int32 subtype;
+Record subtype. Always set to 21.
+
+@item int32 size;
+Always set to 1.
+
+@item int32 count;
+The number of bytes following the header until the next header.
+
+@item int32 var_name_len;
+@itemx char var_name[];
+The number of bytes in the name of the variable that has long string
+value labels, plus the variable name itself, which consists of exactly
+@code{var_name_len} bytes. The variable name is not padded to any
+particular boundary, nor is it null-terminated.
+
+@item int32 var_width;
+The width of the variable, in bytes, which will be between 9 and
+32767.
+
+@item int32 n_labels;
+@itemx long_string_label labels[];
+The long string labels themselves. The @code{labels} array contains
+exactly @code{n_labels} elements, each of which has the following
+substructure:
+
+@example
+int32 value_len;
+char value[];
+int32 label_len;
+char label[];
+@end example
+
+@table @code
+@item int32 value_len;
+@itemx char value[];
+The string value being labeled. @code{value_len} is the number of
+bytes in @code{value}; it is equal to @code{var_width}. The
+@code{value} array is not padded or null-terminated.
+
+@item int32 label_len;
+@itemx char label[];
+The label for the string value. @code{label_len}, which must be
+between 0 and 120, is the number of bytes in @code{label}. The
+@code{label} array is not padded or null-terminated.
+@end table
+@end table
+
+@node Long String Missing Values Record
+@section Long String Missing Values Record
+
+This record, if present, specifies missing values for long string
+variables.
+
+@example
+/* @r{Header.} */
+int32 rec_type;
+int32 subtype;
+int32 size;
+int32 count;
+
+/* @r{Repeated up to exactly @code{count} bytes.} */
+int32 var_name_len;
+char var_name[];
+char n_missing_values;
+long_string_missing_value values[];
+@end example
+
+@table @code
+@item int32 rec_type;
+Record type. Always set to 7.
+
+@item int32 subtype;
+Record subtype. Always set to 22.
+
+@item int32 size;
+Always set to 1.
+
+@item int32 count;
+The number of bytes following the header until the next header.
+
+@item int32 var_name_len;
+@itemx char var_name[];
+The number of bytes in the name of the long string variable that has
+missing values, plus the variable name itself, which consists of
+exactly @code{var_name_len} bytes. The variable name is not padded to
+any particular boundary, nor is it null-terminated.
+
+@item char n_missing_values;
+The number of missing values, either 1, 2, or 3. (This is, unusually,
+a single byte instead of a 32-bit number.)
+
+@item long_string_missing_value values[];
+The missing values themselves. This array contains exactly
+@code{n_missing_values} elements, each of which has the following
+substructure:
+
+@example
+int32 value_len;
+char value[];
+@end example
+
+@table @code
+@item int32 value_len;
+The length of the missing value string, in bytes. This value should
+be 8, because long string variables are at least 8 bytes wide (by
+definition), only the first 8 bytes of a long string variable's
+missing values are allowed to be non-spaces, and any spaces within the
+first 8 bytes are included in the missing value here.
+
+@item char value[];
+The missing value string, exactly @code{value_len} bytes, without
+any padding or null terminator.
+@end table
+@end table
+
+@node Data File and Variable Attributes Records
+@section Data File and Variable Attributes Records
+
+The data file and variable attributes records represent custom
+attributes for the system file or for individual variables in the
+system file, as defined on the DATAFILE ATTRIBUTE (@pxref{DATAFILE
+ATTRIBUTE,,,pspp, PSPP Users Guide}) and VARIABLE ATTRIBUTE commands
+(@pxref{VARIABLE ATTRIBUTE,,,pspp, PSPP Users Guide}), respectively.
+
+@example
+/* @r{Header.} */
+int32 rec_type;
+int32 subtype;
+int32 size;
+int32 count;
+
+/* @r{Exactly @code{count} bytes of data.} */
+char attributes[];
+@end example
+
+@table @code
+@item int32 rec_type;
+Record type. Always set to 7.
+
+@item int32 subtype;
+Record subtype. Always set to 17 for a data file attribute record or
+to 18 for a variable attributes record.
+
+@item int32 size;
+The size of each element in the @code{attributes} member. Always set to 1.
+
+@item int32 count;
+The total number of bytes in @code{attributes}.
+
+@item char attributes[];
+The attributes, in a text-based format.
+
+In record subtype 17, this field contains a single attribute set. An
+attribute set is a sequence of one or more attributes concatenated
+together. Each attribute consists of a name, which has the same
+syntax as a variable name, followed by, inside parentheses, a sequence
+of one or more values. Each value consists of a string enclosed in
+single quotes (@code{'}) followed by a line feed (byte 0x0a). A value
+may contain single quote characters, which are not themselves escaped
+or quoted or required to be present in pairs. There is no apparent
+way to embed a line feed in a value. There is no distinction between
+an attribute with a single value and an attribute array with one
+element.
+
+In record subtype 18, this field contains a sequence of one or more
+variable attribute sets. If more than one variable attribute set is
+present, each one after the first is delimited from the previous by
+@code{/}. Each variable attribute set consists of a long
+variable name,
+followed by @code{:}, followed by an attribute set with the same
+syntax as on record subtype 17.
+
+System files written by @code{Stata 14.1/-savespss- 1.77 by
+S.Radyakin} may include multiple records with subtype 18, one per
+variable that has variable attributes.
+
+The total length is @code{count} bytes.
+@end table
+
+@subheading Example
+
+A system file produced with the following VARIABLE ATTRIBUTE commands
+in effect:
+
+@example
+VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=fred[1]('23') fred[2]('34').
+VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=bert('123').
+@end example
+
+@noindent
+will contain a variable attribute record with the following contents:
+
+@example
+0000 07 00 00 00 12 00 00 00 01 00 00 00 22 00 00 00 |............"...|
+0010 64 75 6d 6d 79 3a 66 72 65 64 28 27 32 33 27 0a |dummy:fred('23'.|
+0020 27 33 34 27 0a 29 62 65 72 74 28 27 31 32 33 27 |'34'.)bert('123'|
+0030 0a 29 |.) |
+@end example
+
+@menu
+* Variable Roles::
+@end menu
+
+@node Variable Roles
+@subsection Variable Roles
+
+A variable's role is represented as an attribute named @code{$@@Role}.
+This attribute has a single element whose values and their meanings
+are:
+
+@table @code
+@item 0
+Input. This, the default, is the most common role.
+@item 1
+Output.
+@item 2
+Both.
+@item 3
+None.
+@item 4
+Partition.
+@item 5
+Split.
+@end table
+
+@node Extended Number of Cases Record
+@section Extended Number of Cases Record
+
+The file header record expresses the number of cases in the system
+file as an int32 (@pxref{File Header Record}). This record allows the
+number of cases in the system file to be expressed as a 64-bit number.
+
+@example
+int32 rec_type;
+int32 subtype;
+int32 size;
+int32 count;
+int64 unknown;
+int64 ncases64;
+@end example
+
+@table @code
+@item int32 rec_type;
+Record type. Always set to 7.
+
+@item int32 subtype;
+Record subtype. Always set to 16.
+
+@item int32 size;
+Size of each element. Always set to 8.
+
+@item int32 count;
+Number of pieces of data in the data part. Alway set to 2.
+
+@item int64 unknown;
+Meaning unknown. Always set to 1.
+
+@item int64 ncases64;
+Number of cases in the file as a 64-bit integer. Presumably this
+could be -1 to indicate that the number of cases is unknown, for the
+same reason as @code{ncases} in the file header record, but this has
+not been observed in the wild.
+@end table
+
+@node Other Informational Records
+@section Other Informational Records
+
+This chapter documents many specific types of extension records are
+documented here, but others are known to exist. PSPP ignores unknown
+extension records when reading system files.
+
+The following extension record subtypes have also been observed, with
+the following believed meanings:
+
+@table @asis
+@item 5
+A set of grouped variables (according to Aapi H@"am@"al@"ainen).
+
+@item 6
+Date info, probably related to USE (according to Aapi H@"am@"al@"ainen).
+
+@item 12
+A UUID in the format described in RFC 4122. Only two examples
+observed, both written by SPSS 13, and in each case the UUID contained
+both upper and lower case.
+
+@item 24
+XML that describes how data in the file should be displayed on-screen.