the javadoc of the XMLlayout class notices about a DTD, which have to be used for validated XML and presents a link to 'doc-files/log4j.dtd', which can not be fulfilled out of the api documentation. Searching around, the missing DTD can be found in the supplied src.zip inside the directory /java/org/apache/log4j/xml.
This problem occurs also for the XMLSample-file. The link on the page jakarta-log4j-1.2.8\docs\api\org\apache\log4j\xml\examples\XMLSample.html refers to jakarta-log4j-1.2.8\docs\api\org\apache\log4j\xml\examples\doc-files\sample1.xml But the files are in jakarta-log4j-1.1.3\jakarta-log4j-1.1.3\src\java\org\apache\log4j\xml\examples\
1.2.12 candidate This is just a javadoc change.
Fixed for 1.3-alpha7.
*** Bug 17227 has been marked as a duplicate of this bug. ***
*** Bug 18122 has been marked as a duplicate of this bug. ***
*** Bug 30819 has been marked as a duplicate of this bug. ***
Fixed on 1.2 branch as well, for 1.2.12rc2.