You can also have more than one configuration file. Note that each file can configure a different, or the same Server instance and is controlled by the "id" attribute. Eg::
java -jar start.jar etc/abcd.xml etc/xyz.xml
If the id of the server is the same in each configuration file, then the same server is configured by each file and the configurations are added together. If the id of the server is different, then each config file will create a new Server instance within the same JVM.
The configuration files may be parametrized with either System properties (using SystemProperty tag) or properties files (using Property tag) passed on the command line. eg
java -Djetty.port=8888 -jar start.jar myjetty.properties etc/abcdjetty.xml etc/xyzother.xml
The jetty configuration format is a simple mapping from XML to java. With this format you can call the methods defined in the javadoc to configure a server. There is a more in-depth look this syntax and the jetty.xml file in the Syntax Reference section.