In the last section, we touched briefly upon the concept of entities. If you recall, both general and parameter entities were used like macros or aliases in XML.

    <!ENTITY % NAME "text that you want to be represented by the entity">

In the real world, you might have something that looked like the following:

    <!ENTITY % full_name "Diego Ramirez Valenzuela Martinez Perez the 5th">

Entities are referenced using a

     %ENTITYNAME;

such as

      <!ENTITY % TAG_NAMES "NAME | EMAIL | PHONE | ADDRESS">
      <!ELEMENT BUSINESS_CONTACT (%TAG_NAMES; | COMPANY_NAME)>

Make sure you remember the semi-colon. I forget this all the time :)

    <!ENTITY % license_agreement
       SYSTEM "http://www.mydomain.com/license.xml">

Be careful that when defining entities, that you define them before using them. Thus, the following would be invalid because the TAG_NAMES alias is defined after it is used.

      <!ELEMENT PERSONAL_CONTACT (%TAG_NAMES; | BIRTHDAY)>
      <!ELEMENT BUSINESS_CONTACT (%TAG_NAMES; | COMPANY_NAME)>
      <!ENTITY % TAG_NAMES "NAME | EMAIL | PHONE | ADDRESS">

      <!ENTITY % ALIAS "text to be aliased">

For example, you might have something like....

      <!ENTITY % NAME "text that you want to be represented">

Using Parameter entities, you can shorted the declarations of other elements and attributes such as:

      <!ENTITY % TAG_NAMES "NAME | EMAIL | PHONE | ADDRESS">
      <!ELEMENT PERSONAL_CONTACT (%TAG_NAMES; | BIRTHDAY)>
      <!ELEMENT BUSINESS_CONTACT (%TAG_NAMES; | COMPANY_NAME)>