The output of the XMLLayout consists of a series of log4j:event elements as defined in the log4j.dtd. It does not output a complete well-formed XML file. The output is designed to be included as an external entity in a separate file to form a correct XML file.

For example, if abc is the name of the file where the XMLLayout ouput goes, then a well-formed XML file would be:

   <?xml version="1.0" ?>

  <!DOCTYPE log4j:eventSet SYSTEM "log4j.dtd" [<!ENTITY data SYSTEM "abc">]>

  <log4j:eventSet version="1.2" xmlns:log4j="http://jakarta.apache.org/log4j/">
          &data;
  </log4j:eventSet>
  

This approach enforces the independence of the XMLLayout and the appender where it is embedded.

The version attribute helps components to correctly intrepret output generated by XMLLayout. The value of this attribute should be "1.1" for output generated by log4j versions prior to log4j 1.2 (final release) and "1.2" for relase 1.2 and later.