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5. API
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# 6. Schema

1
The structural language is defined by a strict XSD schema. Documents not conforming to the schema MUST be rejected by renderers.

### 6.2. xstructural 8.0 Schema

    <?xml version="1.0" encoding="UTF-8" ?>

    <!--
      Copyright © 2021 Mark Raynsford <code@io7m.com> https://www.io7m.com

      Permission to use, copy, modify, and/or distribute this software for any
      purpose with or without fee is hereby granted, provided that the above
      copyright notice and this permission notice appear in all copies.

      THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
      WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
      MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
      SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
      WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
      ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
      IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
    -->

    <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
                elementFormDefault="qualified"
                xmlns:dc="http://purl.org/dc/elements/1.1/"
                xmlns:s="urn:com.io7m.structural:8:0"
                targetNamespace="urn:com.io7m.structural:8:0">

      <xsd:import namespace="http://purl.org/dc/elements/1.1/"
                  schemaLocation="dc.xsd"/>
      <xsd:import namespace="http://www.w3.org/XML/1998/namespace"
                  schemaLocation="xml.xsd"/>

      <xsd:simpleType name="uuidType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A UUID value.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
          <xsd:pattern value="[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}"/>
        </xsd:restriction>
      </xsd:simpleType>

      <xsd:simpleType name="imageTextType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of text that appears in image elements. This is required to be of non-zero length in order to ensure
            that authors add useful text that will then be used in the 'alt' elements of XHTML generated from the document
            sources.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
          <xsd:minLength value="1"/>
        </xsd:restriction>
      </xsd:simpleType>

      <xsd:simpleType name="typeType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of type names. Type names are used to categorize elements and are somewhat analogous to CSS classes,
            except that they are intended to be used for more than just styling documents.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
          <xsd:pattern value="[a-zA-Z][a-zA-Z0-9_\.\-]*"/>
        </xsd:restriction>
      </xsd:simpleType>

      <xsd:attributeGroup name="standardXMLAttributes">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The standard elements expected to appear in XML texts.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:attribute ref="xml:base"/>
        <xsd:attribute ref="xml:lang"/>
      </xsd:attributeGroup>

      <xsd:attributeGroup name="tableOfContentAttributes">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The attributes used to describe tables of content.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attribute name="tableOfContents"
                       use="optional"
                       default="true"
                       type="xsd:boolean">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              If the value of the attribute is 'true', then a table of contents will be generated in the respective element.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="tableOfContentsDepth"
                       use="optional"
                       default="3"
                       type="xsd:positiveInteger">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The maximum relative depth of sections and subsections that will appear in a generated table of contents.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:attributeGroup>

      <xsd:complexType mixed="true"
                       name="ImageType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An element used to describe an image. The text content of the image element SHOULD be used to provide an
            accessible description of the image. This description is expected to be used by screen readers, and may also be
            displayed by browsers if the referenced image cannot be loaded for any reason.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:simpleContent>
          <xsd:extension base="s:imageTextType">
            <xsd:attributeGroup ref="s:standardXMLAttributes"/>

            <xsd:attribute name="type"
                           type="s:typeType"
                           use="optional">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The type of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
            <xsd:attribute name="width"
                           type="xsd:nonNegativeInteger"
                           use="optional">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The width of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
            <xsd:attribute name="height"
                           type="xsd:nonNegativeInteger"
                           use="optional">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The height of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
            <xsd:attribute name="source"
                           type="xsd:anyURI"
                           use="required">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The source location of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
          </xsd:extension>
        </xsd:simpleContent>
      </xsd:complexType>

      <xsd:element name="Image"
                   type="s:ImageType"/>

      <xsd:complexType name="ItemType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An item appearing in a list.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:ListContent"/>
        </xsd:sequence>
        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the list item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Item"
                   type="s:ItemType"/>

      <xsd:group name="ListContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The elements that may appear in list items.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Image"/>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:ListOrdered"/>
          <xsd:element ref="s:ListUnordered"/>
          <xsd:element ref="s:Term"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="ListOrderedType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An ordered list.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Item"/>
        </xsd:sequence>
        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the list.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="ListOrdered"
                   type="s:ListOrderedType"/>

      <xsd:complexType name="ListUnorderedType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An unordered list.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Item"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the list.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="ListUnordered"
                   type="s:ListUnorderedType"/>

      <xsd:complexType name="ColumnType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A description of a column in a table.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the column.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Column"
                   type="s:ColumnType"/>

      <xsd:complexType name="ColumnsType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A set of table column descriptions.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Column"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the columns.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Columns"
                   type="s:ColumnsType"/>

      <xsd:group name="TableContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that may appear in table cells.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:Term"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="CellType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A cell in a table.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:TableContent"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the cell.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Cell"
                   type="s:CellType"/>

      <xsd:complexType name="RowType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A row of cells in a table.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Cell"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the row.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Row"
                   type="s:RowType"/>

      <xsd:complexType name="TableType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A table. A table consists of a list of column definitions, followed by a sequence of rows consisting of the
            table cells.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence>
          <xsd:element ref="s:Columns"/>
          <xsd:sequence minOccurs="1"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Row"/>
          </xsd:sequence>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the table.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Table"
                   type="s:TableType"/>

      <xsd:complexType name="TermType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A term acts as a simple container of one or more words in a sentence. Term elements can be used to denote the
            semantics of words, such as wrapping the name of a mathematical function in a &lt;Term type="function"&gt;
            element.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="s:typeType"
                       name="type"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the term.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Term"
                   type="s:TermType"/>

      <xsd:complexType name="LinkType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Link element describes a link to an element within the current document. Links may only refer to elements that
            contain an appropriate 'id' attribute.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="s:uuidType"
                       name="target"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The target of the link, which must be an element with an appropriate 'id' attribute.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the link.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Link"
                   type="s:LinkType"/>

      <xsd:complexType name="LinkFootnoteType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A LinkFootnote element describes a link to a footnote within the current section.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="s:uuidType"
                       name="target"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The target of the link, which must be a Footnote with a matching 'id' attribute.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the link.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="LinkFootnote"
                   type="s:LinkFootnoteType"/>

      <xsd:complexType name="LinkExternalType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A LinkExternal element describes a link to an external URI.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="xsd:anyURI"
                       name="target"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The target URI.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the link.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="LinkExternal"
                   type="s:LinkExternalType"/>

      <xsd:complexType name="VerbatimType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Verbatim element contains text that should be reproduced exactly, with almost all whitespace intact. Renderers
            are permitted to trim leading and trailing whitespace.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the verbatim text.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Verbatim"
                   type="s:VerbatimType"/>

      <xsd:group name="FormalItemContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that can appear in formal items.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Image"/>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:ListOrdered"/>
          <xsd:element ref="s:ListUnordered"/>
          <xsd:element ref="s:Table"/>
          <xsd:element ref="s:Term"/>
          <xsd:element ref="s:Verbatim"/>
        </xsd:choice>
      </xsd:group>

      <xsd:group name="ParagraphContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that can appear in paragraphs.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:Term"/>
        </xsd:choice>
      </xsd:group>

      <xsd:simpleType name="MetaPropertyNameType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of meta property names.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
          <xsd:pattern value="([a-z0-9_\-]+)(.([a-z0-9_\-]+))+"/>
        </xsd:restriction>
      </xsd:simpleType>

      <xsd:complexType name="MetaPropertyType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A metadata property.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attribute name="name"
                       use="required"
                       type="s:MetaPropertyNameType"/>
        <xsd:attribute name="visible"
                       use="optional"
                       default="false"
                       type="xsd:boolean"/>
      </xsd:complexType>

      <xsd:element name="MetaProperty"
                   type="s:MetaPropertyType"/>

      <xsd:complexType name="MetadataType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An element containing document metadata.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence>
          <xsd:group ref="dc:elementsGroup"/>
          <xsd:sequence minOccurs="0"
                        maxOccurs="unbounded">
            <xsd:element ref="s:MetaProperty"/>
          </xsd:sequence>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
      </xsd:complexType>

      <xsd:element name="Metadata"
                   type="s:MetadataType"/>

      <xsd:complexType name="ParagraphType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A paragraph denotes a self-contained series of sentences.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:ParagraphContent"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the paragraph.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional"/>
      </xsd:complexType>

      <xsd:element name="Paragraph"
                   type="s:ParagraphType"/>

      <xsd:complexType name="FormalItemType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A formal item is analogous to a "figure" in printed text. Formal items are used to significant images, tables of
            data, code listings, and other important objects into texts. They are considered to be at the same level of
            structural significance as paragraphs.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:group ref="s:FormalItemContent"/>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the formal item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the formal item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="title"
                       type="xsd:string"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The title of the formal item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="FormalItem"
                   type="s:FormalItemType"/>

      <xsd:group name="SubsectionContent">
        <xsd:choice>
          <xsd:element ref="s:Paragraph"/>
          <xsd:element ref="s:FormalItem"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="SubsectionType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Subsection is a structural element that denotes a part of the document similar to a chapter.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:sequence minOccurs="1"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Subsection"/>
          </xsd:sequence>
          <xsd:sequence minOccurs="1"
                        maxOccurs="unbounded">
            <xsd:group ref="s:SubsectionContent"/>
          </xsd:sequence>
        </xsd:choice>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the subsection.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the subsection.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="title"
                       type="xsd:string"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The title of the subsection.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Subsection"
                   type="s:SubsectionType"/>

      <xsd:group name="FootnoteContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that may appear in footnotes.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Image"/>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:ListOrdered"/>
          <xsd:element ref="s:ListUnordered"/>
          <xsd:element ref="s:Table"/>
          <xsd:element ref="s:Term"/>
          <xsd:element ref="s:Verbatim"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="FootnoteType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Footnote is a note of referenc or comment usually placed at the bottom of a page. Footnotes may be referenced
            by LinkFootnote elements.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:FootnoteContent"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the footnote.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Footnote"
                   type="s:FootnoteType"/>

      <xsd:complexType name="SectionType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Section is a structural element that denotes a part of the document similar to a chapter. Renderers that
            produce multiple pages MUST insert whatever is analogous to a page break at the end of a section.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence>
          <xsd:choice>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Section"/>
            </xsd:sequence>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Subsection"/>
            </xsd:sequence>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:group ref="s:SubsectionContent"/>
            </xsd:sequence>
          </xsd:choice>
          <xsd:sequence minOccurs="0"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Footnote"/>
          </xsd:sequence>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attributeGroup ref="s:tableOfContentAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the section.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the section.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="title"
                       type="xsd:string"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The title of the section.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Section"
                   type="s:SectionType">

        <xsd:unique name="SectionFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnotes within a section must have unique identifiers.
            </xsd:documentation>
          </xsd:annotation>
          <xsd:selector xpath="s:Footnote"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:keyref name="SectionFootnoteReferencesParagraph"
                    refer="s:SectionFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnote links in paragraphs must refer to footnotes that exist in this section.
            </xsd:documentation>
          </xsd:annotation>
          <xsd:selector xpath="s:Paragraph/*/s:LinkFootnote"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>

        <xsd:keyref name="SectionFootnoteReferencesSubsection"
                    refer="s:SectionFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnote links in subsections must refer to footnotes that exist in this section.
            </xsd:documentation>
          </xsd:annotation>
          <xsd:selector xpath="s:Subsection/*/s:LinkFootnote"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>
      </xsd:element>

      <xsd:complexType name="DocumentType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The Document element represents the top-level structure of a document. The name 'document' is somewhat of a
            misnomer, as nothing prevents the document from being structured as a book (with chapters, etc). The document
            begins with standard Dublin Core metadata, and contains _either_ a series of sections _or_ a series of
            subsections (but not both).
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence>
          <xsd:element ref="s:Metadata"/>
          <xsd:choice>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Section"/>
            </xsd:sequence>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Subsection"/>
            </xsd:sequence>
          </xsd:choice>
          <xsd:sequence minOccurs="0"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Footnote"/>
          </xsd:sequence>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attributeGroup ref="s:tableOfContentAttributes"/>
      </xsd:complexType>

      <xsd:element name="Document"
                   type="s:DocumentType">
        <xsd:unique name="ItemIDsAreUnique">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All 'id' attributes specified on objects within the document must be unique.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath=".//s:FormalItem|.//s:Paragraph|.//s:Subsection|.//s:Section|.//s:Footnote"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:unique name="LinkReferencesAreUnique">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All 'id' attributes specified on objects within the document must be unique.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath=".//s:FormalItem|.//s:Paragraph|.//s:Subsection|.//s:Section"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:keyref name="LinkReferences"
                    refer="s:LinkReferencesAreUnique">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All Link elements must refer to elements with existing 'id' attributes.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath=".//s:Link"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>

        <xsd:unique name="DocumentFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All 'id' attributes specified on footnotes within the document must be unique.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath="s:Footnote"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:keyref name="DocumentFootnoteReferences"
                    refer="s:DocumentFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnote references must refer to footnotes that exist.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath="s:Subsection/*/s:LinkFootnote"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>
      </xsd:element>

    </xsd:schema>

### 6.3. xstructural 7.0 Schema

    <?xml version="1.0" encoding="UTF-8" ?>

    <!--
      Copyright © 2021 Mark Raynsford <code@io7m.com> https://www.io7m.com

      Permission to use, copy, modify, and/or distribute this software for any
      purpose with or without fee is hereby granted, provided that the above
      copyright notice and this permission notice appear in all copies.

      THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
      WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
      MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
      SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
      WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
      ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
      IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
    -->

    <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
                elementFormDefault="qualified"
                xmlns:dc="http://purl.org/dc/elements/1.1/"
                xmlns:s="urn:com.io7m.structural:7:0"
                targetNamespace="urn:com.io7m.structural:7:0">

      <xsd:import namespace="http://purl.org/dc/elements/1.1/"
                  schemaLocation="dc.xsd"/>
      <xsd:import namespace="http://www.w3.org/XML/1998/namespace"
                  schemaLocation="xml.xsd"/>

      <xsd:simpleType name="uuidType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A UUID value.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
          <xsd:pattern value="[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}"/>
        </xsd:restriction>
      </xsd:simpleType>

      <xsd:simpleType name="imageTextType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of text that appears in image elements. This is required to be of non-zero length in order to ensure
            that authors add useful text that will then be used in the 'alt' elements of XHTML generated from the document
            sources.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
          <xsd:minLength value="1"/>
        </xsd:restriction>
      </xsd:simpleType>

      <xsd:simpleType name="typeType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of type names. Type names are used to categorize elements and are somewhat analogous to CSS classes,
            except that they are intended to be used for more than just styling documents.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:restriction base="xsd:string">
          <xsd:pattern value="[a-zA-Z][a-zA-Z0-9_\.\-]*"/>
        </xsd:restriction>
      </xsd:simpleType>

      <xsd:attributeGroup name="standardXMLAttributes">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The standard elements expected to appear in XML texts.
          </xsd:documentation>
        </xsd:annotation>
        <xsd:attribute ref="xml:base"/>
        <xsd:attribute ref="xml:lang"/>
      </xsd:attributeGroup>

      <xsd:attributeGroup name="tableOfContentAttributes">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The attributes used to describe tables of content.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attribute name="tableOfContents"
                       use="optional"
                       default="true"
                       type="xsd:boolean">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              If the value of the attribute is 'true', then a table of contents will be generated in the respective element.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="tableOfContentsDepth"
                       use="optional"
                       default="3"
                       type="xsd:positiveInteger">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The maximum relative depth of sections and subsections that will appear in a generated table of contents.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:attributeGroup>

      <xsd:complexType mixed="true"
                       name="ImageType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An element used to describe an image. The text content of the image element SHOULD be used to provide an
            accessible description of the image. This description is expected to be used by screen readers, and may also be
            displayed by browsers if the referenced image cannot be loaded for any reason.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:simpleContent>
          <xsd:extension base="s:imageTextType">
            <xsd:attributeGroup ref="s:standardXMLAttributes"/>

            <xsd:attribute name="type"
                           type="s:typeType"
                           use="optional">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The type of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
            <xsd:attribute name="width"
                           type="xsd:nonNegativeInteger"
                           use="optional">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The width of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
            <xsd:attribute name="height"
                           type="xsd:nonNegativeInteger"
                           use="optional">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The height of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
            <xsd:attribute name="source"
                           type="xsd:anyURI"
                           use="required">
              <xsd:annotation>
                <xsd:documentation xml:lang="en">
                  The source location of the image.
                </xsd:documentation>
              </xsd:annotation>
            </xsd:attribute>
          </xsd:extension>
        </xsd:simpleContent>
      </xsd:complexType>

      <xsd:element name="Image"
                   type="s:ImageType"/>

      <xsd:complexType name="ItemType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An item appearing in a list.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:ListContent"/>
        </xsd:sequence>
        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the list item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Item"
                   type="s:ItemType"/>

      <xsd:group name="ListContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The elements that may appear in list items.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Image"/>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:ListOrdered"/>
          <xsd:element ref="s:ListUnordered"/>
          <xsd:element ref="s:Term"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="ListOrderedType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An ordered list.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Item"/>
        </xsd:sequence>
        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the list.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="ListOrdered"
                   type="s:ListOrderedType"/>

      <xsd:complexType name="ListUnorderedType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An unordered list.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Item"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the list.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="ListUnordered"
                   type="s:ListUnorderedType"/>

      <xsd:complexType name="ColumnType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A description of a column in a table.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the column.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Column"
                   type="s:ColumnType"/>

      <xsd:complexType name="ColumnsType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A set of table column descriptions.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Column"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the columns.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Columns"
                   type="s:ColumnsType"/>

      <xsd:group name="TableContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that may appear in table cells.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:Term"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="CellType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A cell in a table.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:TableContent"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the cell.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Cell"
                   type="s:CellType"/>

      <xsd:complexType name="RowType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A row of cells in a table.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="1"
                      maxOccurs="unbounded">
          <xsd:element ref="s:Cell"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the row.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Row"
                   type="s:RowType"/>

      <xsd:complexType name="TableType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A table. A table consists of a list of column definitions, followed by a sequence of rows consisting of the
            table cells.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence>
          <xsd:element ref="s:Columns"/>
          <xsd:sequence minOccurs="1"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Row"/>
          </xsd:sequence>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the table.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Table"
                   type="s:TableType"/>

      <xsd:complexType name="TermType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A term acts as a simple container of one or more words in a sentence. Term elements can be used to denote the
            semantics of words, such as wrapping the name of a mathematical function in a &lt;Term type="function"&gt;
            element.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="s:typeType"
                       name="type"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the term.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Term"
                   type="s:TermType"/>

      <xsd:complexType name="LinkType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Link element describes a link to an element within the current document. Links may only refer to elements that
            contain an appropriate 'id' attribute.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="s:uuidType"
                       name="target"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The target of the link, which must be an element with an appropriate 'id' attribute.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the link.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Link"
                   type="s:LinkType"/>

      <xsd:complexType name="LinkFootnoteType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A LinkFootnote element describes a link to a footnote within the current section.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="s:uuidType"
                       name="target"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The target of the link, which must be a Footnote with a matching 'id' attribute.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the link.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="LinkFootnote"
                   type="s:LinkFootnoteType"/>

      <xsd:complexType name="LinkExternalType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A LinkExternal element describes a link to an external URI.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute type="xsd:anyURI"
                       name="target"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The target URI.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the link.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="LinkExternal"
                   type="s:LinkExternalType"/>

      <xsd:complexType name="VerbatimType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Verbatim element contains text that should be reproduced exactly, with almost all whitespace intact. Renderers
            are permitted to trim leading and trailing whitespace.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the verbatim text.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Verbatim"
                   type="s:VerbatimType"/>

      <xsd:group name="FormalItemContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that can appear in formal items.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Image"/>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:ListOrdered"/>
          <xsd:element ref="s:ListUnordered"/>
          <xsd:element ref="s:Table"/>
          <xsd:element ref="s:Term"/>
          <xsd:element ref="s:Verbatim"/>
        </xsd:choice>
      </xsd:group>

      <xsd:group name="ParagraphContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that can appear in paragraphs.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:ListOrdered"/>
          <xsd:element ref="s:ListUnordered"/>
          <xsd:element ref="s:Term"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="MetadataType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            An element containing document metadata.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:group ref="dc:elementsGroup"/>
        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
      </xsd:complexType>

      <xsd:element name="Metadata"
                   type="s:MetadataType"/>

      <xsd:complexType name="ParagraphType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A paragraph denotes a self-contained series of sentences.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:ParagraphContent"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the paragraph.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional"/>
      </xsd:complexType>

      <xsd:element name="Paragraph"
                   type="s:ParagraphType"/>

      <xsd:complexType name="FormalItemType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A formal item is analogous to a "figure" in printed text. Formal items are used to significant images, tables of
            data, code listings, and other important objects into texts. They are considered to be at the same level of
            structural significance as paragraphs.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:group ref="s:FormalItemContent"/>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the formal item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the formal item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="title"
                       type="xsd:string"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The title of the formal item.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="FormalItem"
                   type="s:FormalItemType"/>

      <xsd:group name="SubsectionContent">
        <xsd:choice>
          <xsd:element ref="s:Paragraph"/>
          <xsd:element ref="s:FormalItem"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="SubsectionType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Subsection is a structural element that denotes a part of the document similar to a chapter.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:sequence minOccurs="1"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Subsection"/>
          </xsd:sequence>
          <xsd:sequence minOccurs="1"
                        maxOccurs="unbounded">
            <xsd:group ref="s:SubsectionContent"/>
          </xsd:sequence>
        </xsd:choice>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the subsection.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the subsection.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="title"
                       type="xsd:string"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The title of the subsection.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Subsection"
                   type="s:SubsectionType"/>

      <xsd:group name="FootnoteContent">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The type of content that may appear in footnotes.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:choice>
          <xsd:element ref="s:Image"/>
          <xsd:element ref="s:Link"/>
          <xsd:element ref="s:LinkExternal"/>
          <xsd:element ref="s:LinkFootnote"/>
          <xsd:element ref="s:ListOrdered"/>
          <xsd:element ref="s:ListUnordered"/>
          <xsd:element ref="s:Table"/>
          <xsd:element ref="s:Term"/>
          <xsd:element ref="s:Verbatim"/>
        </xsd:choice>
      </xsd:group>

      <xsd:complexType name="FootnoteType"
                       mixed="true">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Footnote is a note of referenc or comment usually placed at the bottom of a page. Footnotes may be referenced
            by LinkFootnote elements.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence minOccurs="0"
                      maxOccurs="unbounded">
          <xsd:group ref="s:FootnoteContent"/>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the footnote.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Footnote"
                   type="s:FootnoteType"/>

      <xsd:complexType name="SectionType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            A Section is a structural element that denotes a part of the document similar to a chapter. Renderers that
            produce multiple pages MUST insert whatever is analogous to a page break at the end of a section.
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence>
          <xsd:choice>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Section"/>
            </xsd:sequence>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Subsection"/>
            </xsd:sequence>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:group ref="s:SubsectionContent"/>
            </xsd:sequence>
          </xsd:choice>
          <xsd:sequence minOccurs="0"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Footnote"/>
          </xsd:sequence>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attributeGroup ref="s:tableOfContentAttributes"/>

        <xsd:attribute name="type"
                       type="s:typeType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The type of the section.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="id"
                       type="s:uuidType"
                       use="optional">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The unique identifier of the section.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>

        <xsd:attribute name="title"
                       type="xsd:string"
                       use="required">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              The title of the section.
            </xsd:documentation>
          </xsd:annotation>
        </xsd:attribute>
      </xsd:complexType>

      <xsd:element name="Section"
                   type="s:SectionType">

        <xsd:unique name="SectionFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnotes within a section must have unique identifiers.
            </xsd:documentation>
          </xsd:annotation>
          <xsd:selector xpath="s:Footnote"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:keyref name="SectionFootnoteReferencesParagraph"
                    refer="s:SectionFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnote links in paragraphs must refer to footnotes that exist in this section.
            </xsd:documentation>
          </xsd:annotation>
          <xsd:selector xpath="s:Paragraph/*/s:LinkFootnote"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>

        <xsd:keyref name="SectionFootnoteReferencesSubsection"
                    refer="s:SectionFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnote links in subsections must refer to footnotes that exist in this section.
            </xsd:documentation>
          </xsd:annotation>
          <xsd:selector xpath="s:Subsection/*/s:LinkFootnote"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>
      </xsd:element>

      <xsd:complexType name="DocumentType">
        <xsd:annotation>
          <xsd:documentation xml:lang="en">
            The Document element represents the top-level structure of a document. The name 'document' is somewhat of a
            misnomer, as nothing prevents the document from being structured as a book (with chapters, etc). The document
            begins with standard Dublin Core metadata, and contains _either_ a series of sections _or_ a series of
            subsections (but not both).
          </xsd:documentation>
        </xsd:annotation>

        <xsd:sequence>
          <xsd:element ref="s:Metadata"/>
          <xsd:choice>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Section"/>
            </xsd:sequence>
            <xsd:sequence minOccurs="1"
                          maxOccurs="unbounded">
              <xsd:element ref="s:Subsection"/>
            </xsd:sequence>
          </xsd:choice>
          <xsd:sequence minOccurs="0"
                        maxOccurs="unbounded">
            <xsd:element ref="s:Footnote"/>
          </xsd:sequence>
        </xsd:sequence>

        <xsd:attributeGroup ref="s:standardXMLAttributes"/>
        <xsd:attributeGroup ref="s:tableOfContentAttributes"/>
      </xsd:complexType>

      <xsd:element name="Document"
                   type="s:DocumentType">
        <xsd:unique name="ItemIDsAreUnique">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All 'id' attributes specified on objects within the document must be unique.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath=".//s:FormalItem|.//s:Paragraph|.//s:Subsection|.//s:Section|.//s:Footnote"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:unique name="LinkReferencesAreUnique">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All 'id' attributes specified on objects within the document must be unique.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath=".//s:FormalItem|.//s:Paragraph|.//s:Subsection|.//s:Section"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:keyref name="LinkReferences"
                    refer="s:LinkReferencesAreUnique">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All Link elements must refer to elements with existing 'id' attributes.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath=".//s:Link"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>

        <xsd:unique name="DocumentFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All 'id' attributes specified on footnotes within the document must be unique.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath="s:Footnote"/>
          <xsd:field xpath="@id"/>
        </xsd:unique>

        <xsd:keyref name="DocumentFootnoteReferences"
                    refer="s:DocumentFootnoteKey">
          <xsd:annotation>
            <xsd:documentation xml:lang="en">
              All footnote references must refer to footnotes that exist.
            </xsd:documentation>
          </xsd:annotation>

          <xsd:selector xpath="s:Subsection/*/s:LinkFootnote"/>
          <xsd:field xpath="@target"/>
        </xsd:keyref>
      </xsd:element>

    </xsd:schema>

5. API
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