From the website:
Riak Search is a distributed, easily-scalable, failure-tolerant, real-time, full-text search engine built around Riak Core and tightly integrated with Riak KV.
Riak Search allows you to find and retrieve your Riak objects using the objects’ values. When a Riak KV bucket has been enabled for Search integration (by installing the Search pre-commit hook), any objects stored in that bucket are also indexed seamlessly in Riak Search.
The Riak Client API can then be used to perform Search queries that return a list of bucket/key pairs matching the query. Alternatively, the query results can be used as the input to a Riak map/reduce operation. Currently the PHP, Python, Ruby, and Erlang APIs support integration with Riak Search.
The indexing of XML data (it takes path/element name as key) is plausible enough. Made me wonder about a slightly different operation.
What if as part of the indexing operation, additional properties were added to the key?
Could be as simple as the DTD/Schema that defines the element or more complex information about the field.