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diff --git a/spv-file-format.texi b/spv-file-format.texi
index 5eae54df73..3c40e76e21 100644
--- a/spv-file-format.texi
+++ b/spv-file-format.texi
@@ -70,3 +70,22 @@ 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.  The