Example: Constrain attributes for the <section> element

In this scenario, an information architect wants to redefine the attributes for the <section> element. He wants to make the @id attribute required and omit the @spectitle attribute.

  1. He creates a .mod file named idRequiredSectionContraint.mod, where "idRequired" is a string that characterizes the constraint.
  2. He adds the following content to idRequiredSectionContraint.mod:
    <!-- ============================================================= -->
<!--                    CONSTRAINED TOPIC ENTITIES                 -->
<!-- ============================================================= -->

<!ENTITY section-constraints     
  "(topic idRequired-section-c)"
>

<!-- Declares the entities referenced in the constrained content  -->
<!-- model.                                                       -->
<!ENTITY % conref-atts 
             'conref    CDATA #IMPLIED
              conrefend CDATA #IMPLIED
              conaction (mark|pushafter|pushbefore|pushreplace|-dita-use-conref-target) #IMPLIED
              conkeyref CDATA #IMPLIED' >
<!ENTITY % filter-atts
             'props      CDATA #IMPLIED
              platform   CDATA #IMPLIED
              product    CDATA #IMPLIED
              audience   CDATA #IMPLIED
              otherprops CDATA #IMPLIED
              %props-attribute-extensions;' >
<!ENTITY % select-atts 
             '%filter-atts;
              base      CDATA #IMPLIED
              %base-attribute-extensions;
              importance (default|deprecated|high|low|normal|obsolete|optional| 
                          recommended|required|urgent|-dita-use-conref-target) #IMPLIED
              rev       CDATA #IMPLIED
              status     (changed|deleted|unchanged|-dita-use-conref-target) #IMPLIED' >
<!ENTITY % localization-atts 
             'translate (no|yes|-dita-use-conref-target) #IMPLIED
              xml:lang CDATA #IMPLIED
              dir      (lro|ltr|rlo|rtl|-dita-use-conref-target) #IMPLIED' >

<!-- Declares the constrained content model. Original definition   -->
<!-- included %univ-atts;, spectitle, and outputclass; now includes-->
<!-- individual pieces of univ-atts, to make ID required.          -->

<!ENTITY % section.attributes 
          "id          CDATA   #REQUIRED
           %conref-atts;
           %select-atts;
           %localization-atts;
           outputclass CDATA   #IMPLIED">
    Note: The information architect had to declare all the parameter entities that are referenced in the redefined attributes for <section>. If he did not do so, none of the attributes that are declared in the %conref-atts;, %select-atts;, or %localization-atts; parameter entities would be available on the <section> element. Furthermore, since the %select-atts; parameter entity references the %filter-atts; parameter entity, the %filter-atts; must be declared and it must precede the declaration for the %select-atts; parameter entity. The %props-attribute-extensions; and %base-attribute-extensions; parameter entities do not need to be declared in the constraint module, because they are declared in the document-type shells before the inclusion of the constraint module.
  3. He then integrates the constraint module into the applicable document-type shells and adds it to his catalog.xml file.