The conditional section markup provides support for conditionally including and excluding content at parse time within an XML document's external subset. Conditional sections are not allowed within a document's internal subset. The following example illustrates a likely application of conditional sections:

<!ENTITY % debug 'IGNORE' >
<!ENTITY % release 'INCLUDE' >
 
<!ELEMENT addend (#PCDATA)>
<!ELEMENT result (#PCDATA)>
 
<![%debug;[
<!ELEMENT sum (addend+, result)>
]]>
<![%release;[
<!ELEMENT sum (result)>
]]>