Real World XML

Using INCLUDE and IGNORE

Two important DTD directives are often used with parameter entities: INCLUDE and IGNORE. You use these directives to include or remove sections of a DTD; here's how you use them: <![ INCLUDE [DTD Section]]> and <![ IGNORE [DTD Section]]>. Using these directives, you can customize your DTD.

Here's an example showing what these two directives look like in practice:

<![ INCLUDE [ 
<!ELEMENT PRODUCT_ID (#PCDATA)>
<!ELEMENT SHIP_DATE (#PCDATA)>
<!ELEMENT SKU (#PCDATA)>
]]>
<![ IGNORE [
<!ELEMENT PRODUCT_ID (#PCDATA)>
<!ELEMENT SHIP_DATE (#PCDATA)>
<!ELEMENT SKU (#PCDATA)>
]]>

You might wonder what the big deal is here—after all, you can just use a comment to hide sections of a DTD. The usefulness of INCLUDE and IGNORE sections ...