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Introduction to XML For Web Developers
Entities  

To a large degree much of the discussion of entities is more relevant in the next section, writing "valid" documents, rather than in this section, writing "well-formed" documents.

As such, we will discuss entities in greater details in the next section. Nevertheless, some issues make sense within this section, because entities must be well-formed as well as valid. So, in this section, we will introduce entities in terms of their basic syntax and leave the nitty gritty for a little bit later.

As we said before, entities are essentially aliases that allow you to refer to large sections of text without having to type them out every time you want to use them.

Suppose you have your letterhead saved as an entity in a shared file. Then, every time you write a letter in XML, you might say something like

    <LETTER>
    &letterhead;
    <TO>Bob Frog</TO>
    <BODY>
    blah blah blah
    </BODY>
    <FROM>Kevin Kelly</FROM>
    </LETTER>

Notice that the letterhead might expand out to

    My Company
    1234 Fifth Ave.
    Suite 1256
    Los Angeles, California 90026

However, instead of typing that out in every letter, you just use

&letterhead;

There are two types of entities, general and parameter entities and each entity has two parts, the declaration and the entity reference.

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