I have not been setting the system property while using dita-ng. My impression is that the system property is no longer needed (for xerces), at least in the dita-ng that was on googlecode. I guess that must have been done after the slides about dita-ng.
The parameter for Xerces is found in the service provider configuration file in dita-ng.jar:
META-INF/services/org.apache.xerces.xni.parser.XMLParserConfiguration
which contains:
org.ditang.relaxng.defaults.RelaxDefaultsParserConfiguration
As for using the dita command, one way to do this is to set classpath outside of dita to point at dita-ng.jar and jing.jar.
For example, these scripts:
Unix (bash):
export CLASSPATH=`pwd`/plugins/org.dita-ng.doctypes/lib/dita-ng.jar
export CLASSPATH=$CLASSPATH:`pwd`/plugins/org.dita-ng.doctypes/lib/jing.jar
bin/dita $@
Windows:
set CLASSPATH=%CD%\plugins\org.dita-ng.doctypes\lib\dita-ng.jar
set CLASSPATH=%CLASSPATH%:%CD%\plugins\org.dita-ng.doctypes\lib\jing.jar
bin/dita %*
Kendall