The query from sys.dm_os_ring_buffers returns an XML column. The expression "record.value" pulls out some information from a given location within the XML and the "RecordMonitorEvent" is part of the XML returned from the sys.dm_os_ring_buffers table. The whole parameter is basically telling the "record.value" where to find the value to extract from the XML.

If the query just returned the XML then it would be hard to read so it has been formatted nicely so you can read it using the XML queries.

Alex