XML by Example

Conditional Sections

As your DTDs mature, you might have to change them in ways that are

partly incompatible with previous usage. During the migration period,

when you have new and old documents, it is difficult to maintain the DTD.

To help you manage migrations and other special cases, XML provides con-

ditional sections. Conditional sections are included or excluded from the

DTD depending on the value of a keyword. Therefore, you can include or

exclude a large part of a DTD by simply changing one keyword.

Listing 3.13 shows how to use conditional sections. The

strict parameter

entity resolves to INCLUDE. The lenient parameter entity resolves to IGNORE ...