+The @file{@var{prefix}} in the names of the detail members is
+typically an 11-digit decimal number that increases for each item,
+tending to skip values. Older SPV files use different naming
+conventions. Structure member refer to detail members by name, and so
+their exact names do not appear to matter as long as they are unique.
+
+@node SPV Structure Member Format
+@subsection Structure Member Format
+
+Structure members XML files claim conformance with a collection of XML
+Schemas. These schemas are distributed, under a nonfree license, with
+SPSS binaries. Fortunately, the schemas are not necessary to
+understand the structure members. To a degree, the schemas can even
+be deceptive because they document elements and attributes that are
+not in the corpus and lack documentation of elements and attributes
+that are commonly found in the corpus.
+
+Structure members use a different XML namespace for each schema, but
+these namespaces are not entirely consistent: in some SPV files, for
+example, the @code{viewer-tree} schema is associated with namespace
+@indicateurl{http://xml.spss.com/spss/viewer-tree} and in other with
+@indicateurl{http://xml.spss.com/spss/viewer/viewer-tree} (note the
+additional @file{viewer/} directory. In any case, the schema URIs are
+not resolvable to obtain the schemas themselves.
+
+One may ignore all of the above in interpreting a structure member.
+The actual XML has a simple and straightforward form that does not
+require a reader to take schemas or namespaces into account.
+
+@table @code
+@item heading
+Parent: Document root or @code{heading} @*
+Contents: @code{label} [@code{container} | @code{heading}]*
+
+The root of a structure member is a @code{heading}, which represents a
+section of output beginning with a title (the @code{label}) and
+ordinarily followed by a container for content and possibly further
+nested (sub)-sections of output.
+
+@item label
+Parent: @code{heading} or @code{container} @*
+Contents: text
+
+Every @code{heading} and @code{container} holds a @code{label} as its
+first child. The root @code{heading} in a structure member always
+contains the string ``Output''. Otherwise, the text in @code{label}
+describes what it labels, often by naming the statistical procedure
+that was executed, e.g.@: ``Frequencies'' or ``T-Test''. Labels are
+often very generic, especially within a @code{container}, e.g.@:
+``Title'' or ``Warnings'' or ``Notes''. Label text is localized
+according to the output language, e.g. in Italian a frequency table
+procedure is labeled ``Frequenze''.
+
+The corpus contains one example of an empty label, one that contains
+no text.
+
+@item container
+Parent: @code{heading} @*
+Contents: @code{label} [@code{table} | @code{text}]
+
+A @code{container} is the immediate parent of a
+@end table