An OntolicaProperty object that represents
the grouping to use on the search results.
Remarks
Although that you can specify any property here then you should
stick to properties that have a limited range of values. E.g.
the Author property. Do not specify a property for which each
document has a unique value. This will result in a group for each
search result.
Ontolica provides special support for the properties Created,
Modified and Size as defined in the default Ontolica
search configuration.