+
+All elements have an optional @code{id} attribute. In practice many
+elements are assigned @code{id} attributes that are never referenced.
+
+@menu
+* SPV Detail visualization Element::
+* SPV Detail userSource Element::
+* SPV Detail sourceVariable Element::
+* SPV Detail derivedVariable Element::
+* SPV Detail extension Element::
+* SPV Detail graph Element::
+* SPV Detail location Element::
+* SPV Detail coordinates Element::
+* SPV Detail faceting Element::
+* SPV Detail facetLayout Element::
+@end menu
+
+@node SPV Detail visualization Element
+@subsection The @code{visualization} Element
+
+@format
+Parent: Document root
+Contents:
+ extension?
+ userSource
+ (sourceVariable @math{|} derivedVariable)@math{+}
+ graph
+ labelFrame@math{+}
+ container?
+ style@math{+}
+ layerController?
+@end format
+
+This element has the following attributes.
+
+@defvr {Required} creator
+The version of the software that created this SPV file, as a string of
+the form @code{xxyyzz}, which represents software version xx.yy.zz,
+e.g.@: @code{160001} is version 16.0.1. The corpus includes major
+versions 16 through 19.
+@end defvr
+
+@defvr {Required} date
+The date on the which the file was created, as a string of the form
+@code{YYYY-MM-DD}.
+@end defvr
+
+@defvr {Required} lang
+The locale used for output, in Windows format, which is similar to the
+format used in Unix with the underscore replaced by a hyphen, e.g.@:
+@code{en-US}, @code{en-GB}, @code{el-GR}, @code{sr-Cryl-RS}.
+@end defvr
+
+@defvr {Required} name
+The title of the pivot table, localized to the output language.
+@end defvr
+
+@defvr {Required} style
+The @code{id} of a @code{style} element (@pxref{SPV Detail style
+element}). This is the base style for the entire pivot table. In
+every example in the corpus, the value is @code{visualizationStyle}
+and the corresponding @code{style} element has no attributes other
+than @code{id}.
+@end defvr
+
+@defvr {Required} type
+A floating-point number. The meaning is unknown.
+@end defvr
+
+@defvr {Required} version
+The visualization schema version number. In the corpus, the value is
+one of 2.4, 2.5, 2.7, and 2.8.
+@end defvr
+
+@node SPV Detail userSource Element
+@subsection The @code{userSource} Element
+
+Parent: @code{visualization} @*
+Contents:
+
+This element has the following attributes.
+
+@defvr {Optional} missing
+Always @code{listwise}.
+@end defvr
+
+@node SPV Detail sourceVariable Element
+@subsection The @code{sourceVariable} Element
+
+Parent: @code{visualization} @*
+Contents: @code{extension}* (@code{format} @math{|} @code{stringFormat})?
+
+This element defines a variable whose values can be used elsewhere in
+the visualization. It ties this element's @code{id} to a variable
+from the @file{tableData.bin} member that corresponds to this
+@file{.xml}.
+
+This element has the following attributes.
+
+@defvr {Required} categorical
+Always set to @code{true}.
+@end defvr
+
+@defvr {Required} source
+Always set to @code{tableData}, the @code{source-name} in the
+corresponding @file{tableData.bin} member (@pxref{SPV Legacy Member
+Metadata}).
+@end defvr
+
+@defvr {Required} sourceName
+The name of a variable within the source, the @code{variable-name} in
+the corresponding @file{tableData.bin} member (@pxref{SPV Legacy
+Member Data}).
+@end defvr
+
+@defvr {Optional} dependsOn
+The @code{variable-name} of a variable linked to this one, so that a
+viewer can work with them together. For a group variable, this is the
+name of the corresponding categorical variable.
+@end defvr
+
+@defvr {Optional} label
+The variable label, if any
+@end defvr
+
+@defvr {Optional} labelVariable
+The @code{variable-name} of a variable whose string values correspond
+one-to-one with the values of this variable and are suitable for use
+as value labels.
+@end defvr
+
+@node SPV Detail derivedVariable Element
+@subsection The @code{derivedVariable} Element
+
+Parent: @code{visualization} @*
+Contents: @code{extension}* (@code{format} @math{|} @code{stringFormat} @code{valueMapEntry}*)
+
+Like @code{sourceVariable}, this element defines a variable whose
+values can be used elsewhere in the visualization. Instead of being
+read from a data source, the variable's data are defined by a
+mathematical expression.
+
+This element has the following attributes.
+
+@defvr {Required} categorical
+Always set to @code{true}.
+@end defvr
+
+@defvr {Required} value
+An expression that defines the variable's value. In theory this could
+be an arbitrary expression in terms of constants, functions, and other
+variables, e.g.@: @math{(@var{var1} + @var{var2}) / 2}. In practice,
+the corpus contains only the following forms of expressions:
+
+@table @code
+@item constant(@var{number})
+@itemx constant(@var{variable})
+A constant. The meaning when a variable is named is unknown.
+Sometimes the ``variable name'' has spaces in it.
+
+@item map(@var{variable})
+Transforms the values in the named @var{variable} using the
+@code{valueMapEntry}s contained within the element.
+@end table
+@end defvr
+
+@defvr {Optional} dependsOn
+The @code{variable-name} of a variable linked to this one, so that a
+viewer can work with them together. For a group variable, this is the
+name of the corresponding categorical variable.
+@end defvr
+
+@menu
+* SPV Detail valueMapEntry Element::
+@end menu
+
+@node SPV Detail valueMapEntry Element
+@subsubsection The @code{valueMapEntry} Element
+
+Parent: @code{derivedVariable} @*
+Contents: empty
+
+A @code{valueMapEntry} element defines a mapping from one or more
+values of a source expression to a target value. (In the corpus, the
+source expression is always just the name of a variable.) Each target
+value requires a separate @code{valueMapEntry}. If multiple source
+values map to the same target value, they can be combined or separate.
+
+@code{valueMapEntry} has the following attributes.
+
+@defvr {Required} from
+A source value, or multiple source values separated by semicolons,
+e.g.@: @code{0} or @code{13;14;15;16}.
+@end defvr
+
+@defvr {Required} to
+The target value.
+@end defvr
+
+@node SPV Detail extension Element
+@subsection The @code{extension} Element
+
+This is a general-purpose ``extension'' element. Readers that don't
+understand a given extension should be able to safely ignore it. The
+attributes on this element, and their meanings, vary based on the
+context. Each known usage is described separately below. The current
+extensions use attributes exclusively, without any nested elements.
+
+@subsubheading @code{visualization} Parent Element
+
+With @code{visualization} as its parent element, @code{extension} has
+the following attributes.
+
+@defvr {Optional} numRows
+An integer that presumably defines the number of rows in the displayed
+pivot table.
+@end defvr
+
+@defvr {Optional} showGridline
+Always set to @code{false} in the corpus.
+@end defvr
+
+@defvr {Optional} minWidthSet
+@defvrx {Optional} maxWidthSet
+Always set to @code{true} in the corpus.
+@end defvr
+
+@subsubheading @code{container} Parent Element
+
+With @code{container} as its parent element, @code{extension} has the
+following attributes.
+
+@defvr {Required} combinedFootnotes
+Always set to @code{true} in the corpus.
+@end defvr
+
+@subsubheading @code{sourceVariable} and @code{derivedVariable} Parent Element
+
+With @code{sourceVariable} or @code{derivedVariable} as its parent
+element, @code{extension} has the following attributes. A given
+parent element often contains several @code{extension} elements that
+specify the meaning of the source data's variables or sources, e.g.@:
+
+@example
+<extension from="0" helpId="corrected_model"/>
+<extension from="3" helpId="error"/>
+<extension from="4" helpId="total_9"/>
+<extension from="5" helpId="corrected_total"/>
+@end example
+
+@defvr {Required} from
+An integer or a name like ``dimension0''.
+@end defvr
+
+@defvr {Required} helpId
+An identifier.
+@end defvr
+
+@node SPV Detail graph Element
+@subsection The @code{graph} Element
+
+Parent: @code{visualization} @*
+Contents: @code{location}@math{+} @code{coordinates} @code{faceting} @code{facetLayout} @code{interval}
+
+@code{graph} has the following attributes.
+
+@defvr {Required} cellStyle
+@defvrx {Required} style
+Each of these is the @code{id} of a @code{style} element (@pxref{SPV
+Detail style element}). The former is the default style for
+individual cells, the latter for the entire table.
+@end defvr
+
+@node SPV Detail location Element
+@subsection The @code{location} Element
+
+Parent: @code{graph} @*
+Contents: empty
+
+Each instance of this element specifies where some part of the table
+frame is located. All the examples in the corpus have four instances
+of this element, one for each of the parts @code{height},
+@code{width}, @code{left}, and @code{top}. Some examples in the
+corpus add a fifth for part @code{bottom}, even though it is not clear
+how all of @code{top}, @code{bottom}, and @code{heigth} can be honored
+at the same time. In any case, @code{location} seems to have little
+importance in representing tables; a reader can safely ignore it.
+
+@defvr {Required} part
+One of @code{height}, @code{width}, @code{top}, @code{bottom}, or
+@code{left}. Presumably @code{right} is acceptable as well but the
+corpus contains no examples.
+@end defvr
+
+@defvr {Required} method
+How the location is determined:
+
+@table @code
+@item sizeToContent
+Based on the natural size of the table. Observed only for
+parts @code{height} and @code{width}.
+
+@item attach
+Based on the location specified in @code{target}. Observed only for
+parts @code{top} and @code{bottom}.
+
+@item fixed
+Using the value in @code{value}. Observed only for parts @code{top},
+@code{bottom}, and @code{left}.
+
+@item same
+Same as the specified @code{target}. Observed only for part
+@code{left}.
+@end table
+@end defvr
+
+@defvr {Optional} min
+Minimum size. Only observed with value @code{100pt}. Only observed
+for part @code{width}.
+@end defvr
+
+@defvr {Dependent} target
+Required when @code{method} is @code{attach} or @code{same}, not
+observed otherwise. This is the ID of an element to attach to.
+Observed with the ID of @code{title}, @code{footnote}, @code{graph},
+and other elements.
+@end defvr
+
+@defvr {Dependent} value
+Required when @code{method} is @code{fixed}, not observed otherwise.
+Observed values are @code{0%}, @code{0px}, @code{1px}, and @code{3px}
+on parts @code{top} and @code{left}, and @code{100%} on part
+@code{bottom}.
+@end defvr
+
+@node SPV Detail coordinates Element
+@subsection The @code{coordinates} Element
+
+Parent: @code{graph} @*
+Contents: empty
+
+This element is always present and always empty, with no attributes
+(except @code{id}).
+
+@node SPV Detail faceting Element
+@subsection The @code{faceting} Element
+
+Parent: @code{graph} @*
+Contents: @code{cross} @code{layer}*
+
+The @code{faceting} element describes the row, column, and layer
+structure of the table. Its @code{cross} child determines the row and
+column structure, and each @code{layer} child (if any) represents a
+layer.
+
+@code{faceting} has no attributes (other than @code{id}).
+
+@subsubheading The @code{cross} Element
+
+Parent: @code{faceting} @*
+Contents: @code{nest} @code{nest}
+
+The @code{cross} element describes the row and column structure of the
+table. It has exactly two @code{nest} children, the first of which
+describes the table's rows and the second the table's columns.
+
+@code{cross} has no attributes (other than @code{id}).
+
+@subsubheading The @code{nest} Element
+
+Parent: @code{cross} @*
+Contents: @code{variableReference}@math{+}
+
+A given @code{nest} usually consists of one or more dimensions, each
+of which is represented by @code{variableReference} child elements.
+Minimally, a dimension has two @code{variableReference} children, one
+for the categories, one for the data, e.g.:
+
+@example
+<nest>
+ <variableReference ref="dimension0categories"/>
+ <variableReference ref="dimension0"/>
+</nest>
+@end example
+
+@noindent
+Groups of categories introduce additional variable references, e.g.@:
+
+@example
+<nest>
+ <variableReference ref="dimension0categories"/>
+ <variableReference ref="dimension0group0"/>
+ <variableReference ref="dimension0"/>
+</nest>
+@end example
+
+@noindent
+Grouping can be hierarchical, e.g.@:
+
+@example
+<nest>
+ <variableReference ref="dimension0categories"/>
+ <variableReference ref="dimension0group1"/>
+ <variableReference ref="dimension0group0"/>
+ <variableReference ref="dimension0"/>
+</nest>
+@end example
+
+@noindent
+XXX what are group maps?
+
+@example
+<nest id="nest_1973">
+ <variableReference ref="dimension1categories"/>
+ <variableReference ref="dimension1group1map"/>
+ <variableReference ref="dimension1group0map"/>
+ <variableReference ref="dimension1"/>
+</nest>
+<nest>
+ <variableReference ref="dimension0categories"/>
+ <variableReference ref="dimension0group0map"/>
+ <variableReference ref="dimension0"/>
+</nest>
+@end example
+
+@noindent
+A @code{nest} can contain multiple dimensions:
+
+@example
+<nest>
+ <variableReference ref="dimension1categories"/>
+ <variableReference ref="dimension1group0"/>
+ <variableReference ref="dimension1"/>
+ <variableReference ref="dimension0categories"/>
+ <variableReference ref="dimension0"/>
+</nest>
+@end example
+
+One @code{nest} within a given @code{cross} may have no dimensions, in
+which case it still has one @code{variableReference} child, which
+references a @code{derivedVariable} whose @code{value} attribute is
+@code{constant(0)}. In the corpus, such a @code{derivedVariable} has
+@code{row} or @code{column}, respectively, as its @code{id}.
+
+@code{nest} has no attributes (other than @code{id}).
+
+@subsubheading The @code{variableReference} Element
+
+Parent: @code{nest} @*
+Contents: empty
+
+@code{variableReference} has one attribute.
+
+@defvr {Required} ref
+The @code{id} of a @code{sourceVariable} or @code{derivedVariable}
+element.
+@end defvr
+
+@subsubheading The @code{layer} Element
+
+Parent: @code{faceting} @*
+Contents: empty
+
+Each layer is represented by a pair of @code{layer} elements. The
+first of this pair is for a category variable, the second for the data
+variable, e.g.:
+
+@example
+<layer value="0" variable="dimension0categories" visible="true"/>
+<layer value="dimension0" variable="dimension0" visible="false"/>
+@end example
+
+@noindent
+@code{layer} has the following attributes.
+
+@defvr {Required} variable
+The @code{id} of a @code{sourceVariable} or @code{derivedVariable}
+element.
+@end defvr
+
+@defvr {Required} value
+The value to select. For a category variable, this is always
+@code{0}; for a data variable, it is the same as the @code{variable}
+attribute.
+@end defvr
+
+@defvr {Optional} visible
+Whether the layer is visible. Generally, category layers are visible
+and data layers are not, but sometimes this attribute is omitted.
+@end defvr
+
+@defvr {Optional} method
+When present, this is always @code{nest}.
+@end defvr
+
+@node SPV Detail facetLayout Element
+@subsection The @code{facetLayout} Element
+
+Parent: @code{graph} @*
+Contents: @code{tableLayout} @code{facetLevel}@math{+} @code{setCellProperties}*
+
+@subsubheading The @code{tableLayout} Element
+
+Parent: @code{facetLayout} @*
+Contents: empty
+
+@defvr {Required} verticalTitlesInCorner
+Always set to @code{true}.
+@end defvr
+
+@defvr {Optional} style
+The @code{id} of a @code{style} element.
+@end defvr
+
+@defvr {Optional} fitCells
+Always set to @code{ticks}.
+@end defvr
+
+@subsubheading The @code{facetLevel} Element
+
+Parent: @code{facetLayout}
+Contents: @code{axis}
+
+Each @code{facetLevel} describes a @code{variableReference} or
+@code{layer}, and a table has one @code{facetLevel} element for
+each such element. For example, an SPV detail member that contains
+four @code{variableReference} elements and two @code{layer} elements
+will contain six @code{facetLevel} elements.
+
+In the corpus, @code{facetLevel} elements and the elements that they
+describe are always in the same order. The correspondence may also be
+observed in two other ways. First, one may use the @code{level}
+attribute, described below. Second, in the corpus, a
+@code{facetLevel} always has an @code{id} that is the same as the
+@code{id} of the element it describes with @code{_facetLevel}
+appended. One should not formally rely on this, of course, but it is
+usefully indicative.
+
+@defvr {Required} level
+A 1-based index into the @code{variableReference} and @code{layer}
+elements, e.g.@: a @code{facetLayout} with a @code{level} of 1
+describes the first @code{variableReference} in the SPV detail member,
+and in a member with four @code{variableReference} elements, a
+@code{facetLayout} with a @code{level} of 5 describes the first
+@code{layer} in the member.
+@end defvr
+
+@defvr {Required} gap
+Always observed as @code{0pt}.
+@end defvr
+
+@subsubheading The @code{setCellProperties} Element
+
+Parent: @code{facetLayout} @*
+Contents: @code{setMetaData} @code{setStyle}* @code{setFormat}@math{+} @code{union}?
+
+This element sets style properties of cells designated by the
+@code{target} attribute of its child elements.
+
+@defvr {Optional} applyToConverse
+If present, always @code{true}. This appears to invert the meaning of
+the @code{target} of sub-elements: the selected cells are the ones
+@emph{not} designated by @code{target}.
+@end defvr
+
+@subsubheading The @code{setMetaData} Element
+
+Parent: @code{setCellProperties} @*
+Contents: empty
+
+It's really not clear what visible effect this element has, if any.
+
+@defvr {Required} target
+The @code{id} of an element whose metadata is to be set. In the
+corpus, this is always @code{graph}, the @code{id} used for the
+@code{graph} element.
+@end defvr
+
+@defvr {Required} key
+@defvrx {Required} value
+A key-value pair to set for the target.
+
+In the corpus, @code{key} is @code{cellPropId} or, rarely,
+@code{diagProps}, and @code{value} is always the @code{id} of the
+parent @code{setCellProperties}.
+@end defvr
+
+@subsubheading The @code{setStyle} Element
+
+Parent: @code{setCellProperties} @*
+Contents: empty
+
+This element associates a style with the target.
+
+@defvr {Required} target
+The @code{id} of an element whose style is to be set. In the corpus,
+this is always the @code{id} of an @code{interval}, @code{labeling},
+or, rarely, @code{graph} element.
+@end defvr
+
+@defvr {Required} style
+The @code{id} of a @code{style} element that identifies the style to
+set on the target.
+@end defvr
+
+@subsubheading The @code{setFormat} Element
+
+@format
+Parent: @code{setCellProperties}
+Contents:
+ @code{format}
+ @math{|} @code{numberFormat}
+ @math{|} @code{stringFormat}@math{+}
+ @math{|} @code{dateTimeFormat}
+@end format
+
+This element sets the format of the target, ``format'' in this case
+meaning an the SPSS print format for a variable.
+
+The details of this element vary depending on the schema version, as
+declared in the root @code{visualization} element's @code{version}
+attribute (@pxref{SPV Detail visualization Element}). In version 2.5
+and earlier, @code{setFormat} contains one of a number of child
+elements that correspond to the different varieties of print formats.
+In version 2.7 and later, @code{setFormat} instead always contains a
+@code{format} element.
+
+@subsubheading The @code{format} Element
+
+Parent: @code{sourceVariable}, @code{derivedVariable}, @code{formatMapping}, @code{labeling}, @code{formatMapping}, @code{setFormat} @*
+Contents: (@code{affix}@math{+} @math{|} @code{relabel})?
+
+This element determines a format, equivalent to an SPSS print format.
+The following attribute determines the high-level kind of formatting
+in use:
+
+@defvr {Optional} baseFormat
+One of @code{date}, @code{time}, @code{dateTime}, or
+@code{elapsedTime}. When this attribute is omitted, this element is a
+numeric or string format.
+@end defvr
+
+@noindent
+Whether other attributes are required (``yes''), prohibited (``no''),
+or optional (``opt'') depends on @code{baseFormat}:
+
+@multitable {maximumFractionDigits} {@code{dateTime}} {@code{elapsedTime}} {number} {string}
+@headitem Attribute @tab @code{dateTime} @tab @code{elapsedTime} @tab number @tab string
+@item errorCharacter @tab yes @tab yes @tab yes @tab opt
+@item maximumFractionDigits @tab no @tab yes @tab yes @tab no
+@item minimumFractionDigits @tab no @tab yes @tab yes @tab no
+@item separatorChars @tab yes @tab no @tab no @tab no
+@item
+@item useGrouping @tab no @tab opt @tab no @tab no
+@item mdyOrder @tab yes @tab no @tab no @tab no
+@item
+@item showYear @tab yes @tab no @tab no @tab no
+@item yearAbbreviation @tab yes @tab no @tab no @tab no
+@item
+@item showMonth @tab yes @tab no @tab no @tab no
+@item monthFormat @tab yes @tab no @tab no @tab no
+@item
+@item showDay @tab yes @tab opt @tab no @tab no
+@item dayPadding @tab yes @tab opt @tab no @tab no
+@item dayOfMonthPadding @tab yes @tab no @tab no @tab no
+@item dayType @tab yes @tab no @tab no @tab no
+@item
+@item showHour @tab yes @tab opt @tab no @tab no
+@item hourFormat @tab yes @tab opt @tab no @tab no
+@item hourPadding @tab yes @tab yes @tab no @tab no
+@item
+@item showMinute @tab yes @tab no @tab no @tab no
+@item minutePadding @tab yes @tab yes @tab no @tab no
+@item
+@item showSecond @tab yes @tab yes @tab no @tab no
+@item secondPadding @tab no @tab yes @tab no @tab no
+@item
+@item showMillis @tab no @tab yes @tab no @tab no
+@item
+@item tryStringsAsNumbers @tab no @tab no @tab no @tab no
+@item
+@item minimumIntegerDigits @tab no @tab no @tab yes @tab no
+@item scientific @tab no @tab no @tab yes @tab no
+@item small @tab no @tab no @tab opt @tab no
+@item
+@item suffix @tab no @tab no @tab opt @tab no
+@end multitable