iCM's CSSearchMultiple class provides access to the SOLR search engine. These articles expand upon the API documentation to look at faceting, grouping, and various location-based searches. Full API documentation for CSSearchMultiple and the iCMAPI Worker can be found in the documentation for your release of iCM.
These article focus on using CSSearchMultiple via the API Server's iCMAPI Worker. They will be of interest to developers working directly with SOLR in the iCM.NET or iCM4j frameworks, although in those frameworks you'll be able to use the various add methods rather than being restricted to working through the request properties.