What about entities?
The concept of entity is valid in writing either XML, DTD, or
XSL. There are two possible entities:
Internal: The piece of code referred is directly written in the entity
External: allows the definition of a variable referencing an external
piece of code. This entity will be used later and replace by the
referred piece of code when the document is processed.
<!ENTITY mdk-co "<company>MandrakeSoft</company>">
<!ENTITY LM "<application>Linux-Mandrake</application>">
&LM; is made by &mdk-co;.
<!ENTITY entity-example SYSTEM "xml-entity-example.xml">
We already saw an example of entity in the previous DTD,
this is an example in XML: