Cascading index engine allows to combine multiple engines behind a singular
IndexEngine interface.
The order of index engines is important is evaluated "left to right", i.e. those added earlier will be given a higher
priority. The way cascading works is if an index engine in the list does not support a specific type of index,
next one in the list will be tried, until the list is exhausted.
In an OSGi environment, indexEngine
property must be configured to ensure intended ordering. This property
should have a comma-delimited list of fully qualified class names for index engines to be used. It can list index engines
that are not available through references. They will be ignored.