The <container/> element has a default attribute. If default="true", then this container will be started if no arquillian.launcher container name is specified.
The <group/> element is used to define a group of containers to be started. However, the group element has no "default" attribute (see http://www.jboss.org/schema/arquillian/arquillian-1.0.xsd). So, if we have a configuration involving a single container and as group of containers in the same arquillian.xml file, such as:
then we cannot make Y the default.
We should be able to specify that a group configuration is the default to be started among a set of configurations, and so group should have a default attribute as well.
NOTE: when used within a <group/> the "default" attribute of container changes its meaning. According to AK:
"default="true" on a /container means this is the default Configuration used if no arquillian.launch is specified. While for a Group it's the default container to use if no @TargetsContainer is used."