Constructing a Document Type Definition (DTD) for XML

The purpose of a parameter entity is to serve as a shorthand for some or all of the content part of an element declaration.

The general form is:

    <!ENTITY % ename "text">

For example, suppose you have a lot of tags whose content model is "#PCDATA|bold|ital)*". You could define an entity like this:

    <!ENTITY bitext "(#PCDATA|bold|ital)*">

Then, to define an element <excuse> with that content:

    <!ELEMENT excuse %bitext;>