Element Domain Specialization Step 2: Declare The Domain Element Types
Step 2-1. Create New .mod File
Step 2-3. Declare Elements and Attributes

Step 2-2. Declare Element Type Name Parameter Entities

For each element type, declare a parameter entity that reflects the element type name: 
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     XML Construct Domain Module
    
     Author: your name here

     Copyright (c) 2011 copyright holder
     
     license to use or not use or whatever
     
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<!ENTITY % xmlelem    "xmlelem"  >

These entities allow the element type to be used in content models via the parameter entity. Document type shells can then integrate further specializations of this element type by redeclaring the parameter entity to include specializations of the element, which then are automatically allowed wherever the base element type is allowed. You can also use the parameter entity in constraint modules to specifically allow only the element type in place of its base type.