Example: Constrain a domain module using DTD

This section is non-normative.

In this scenario, a DITA architect wants to use only a subset of the elements defined in the highlighting domain. They want to use <b> and <i> but not any other of the elements in the domain. They want to integrate this constraint into the document-type shell for task.

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

• Use <b> and <i>
• Remove <line-through>, <overline>, <sup>, <sup>, <tt>, and <u>

1. The DITA architect creates a constraint module: acme-HighlightDomainConstraint.mod.
2. They add the following content to acme-HighlightDomainConstraint.mod:

   <!-- ============================================================= -->
   <!--      CONSTRAINED HIGHLIGHT DOMAIN ENTITIES                    -->
   <!-- ============================================================= -->
   
   <!ENTITY % HighlightingDomain-c-ph     "b | i"                 >  

3. They add the constraint module to the catalog.xml file.
4. They then integrate the constraint module into the company-specific, document-type shell for the task topic by adding the content in the "DOMAIN CONSTRAINT INTEGRATION" section:

   <!-- ============================================================= -->
   <!--                    DOMAIN CONSTRAINT INTEGRATION              -->
   <!-- ============================================================= -->
   
   <!ENTITY % HighlightDomain-c-dec  
     PUBLIC "-//ACME//ENTITIES DITA Highlighting Domain Constraint//EN" 
     "acme-HighlightDomainConstraint.mod"
   >%HighlightDomain-c-dec;

5. In the "DOMAIN EXTENSIONS" section, they replace the parameter entity for the highlighting domain with the parameter entity for the constrained highlighting domain:

   <!ENTITY % ph           "ph |
                            %HighlightDomain-c-ph; |
                            %sw-d-ph; | 
                            %ui-d-ph;
                           ">

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