This class manages all xml merge interactions with callers. It is responsible for
not only loading the handler configurations, but also for cycling through the handlers
in a prioritized fashion and exporting the final merged document.
public static final String MERGE_DEFINITION_SYSTEM_PROPERTY
Additional merge points may be added by the caller. Also default merge points
may be overriden to change their current behavior. This is accomplished by
specifying the system property denoted by the key MergeManager.MERGE_DEFINITION_SYSTEM_PROPERTY
with a value stating the fully qualified path of user-created property file. Please refer
to the default properties file located at org/broadleafcommerce/profile/extensibility/context/merge/default.properties
for more details.