Example: Restrict the content model for the `<topic>` element using RNG

This section is non-normative.

In this scenario, the DITA architect for Acme Incorporated wants to redefine the content model for the topic document type. They want to omit certain elements, make the <shortdesc> element required, and disallow topic nesting.

Specifically, the DITA architect wants to redefine the content model in the following ways:

Remove <abstract>
Require <shortdesc>
Remove <related-links>
Remove the task-info-typespattern in order to disallow topic nesting

The DITA architect creates a constraint module: acme-TopicConstraintMod.rng.
They update the catalog.xml file to include the new constraint module.

They add the following content to acme-TopicConstraint.mod:

<div>
  <a:documentation>CONTENT MODEL OVERRIDES</a:documentation>
  <include href="urn:pubid:oasis:names:tc:dita:rng:topicMod.rng:2.0">
    <define name="topic.content" combine="interleave">
      <ref name="title"/>
      <ref name="shortdesc"/>
      <optional>
        <ref name="prolog"/>
      </optional>
      <optional>
        <ref name="body"/>
      </optional>
    </define>
  </include>
</div>

They then integrate the constraint module into the document-type shell for topic by adding an <include> element in the "ELEMENT-TYPE CONFIGURATION INTEGRATION" section:
```
<div>
  <a:documentation>ELEMENT-TYPE CONFIGURATION INTEGRATION</a:documentation>
  <include href="acme-TopicConstraintMod.rng"/>
</div>
```

They then remove the <include> statement that references topicMod.rng from the "MODULE INCLUSIONS" section:

<div>
  <a:documentation>MODULE INCLUSIONS </a:documentation>
    <include href="urn:pubid:oasis:names:tc:dita:rng:topicMod.rng:2.0"/>
    <include href="urn:pubid:oasis:names:tc:dita:rng:audienceAttDomain.rng:2.0"/>
    <include href="urn:pubid:oasis:names:tc:dita:rng:deliveryTargetAttDomain.rng:2.0"/>
    <include href="urn:pubid:oasis:names:tc:dita:rng:platformAttDomain.rng:2.0"/>
    <include href="urn:pubid:oasis:names:tc:dita:rng:productAttDomain.rng:2.0"/>
    <include href="urn:pubid:oasis:names:tc:dita:rng:otherpropsAttDomain.rng:2.0"/>
    <include href="urn:pubid:oasis:names:tc:dita:rng:highlightDomain.rng:2.0"/>
  </div>

They check their test topic to ensure that the content model is modified as expected.

Example: Restrict the content model for the <topic> element using RNG

Example: Restrict the content model for the `<topic>` element using RNG