Specifies a specific source for a SecurityListType. Relevant when a certain type can be provided from various sources.
1 = ICB (Industry Classification Benchmark) published by Dow Jones and FTSE - www.icbenchmark.com
2 = NAICS (North American Industry Classification System). Replaced SIC (Standard Industry Classification) www.census.gov/naics or www.naics.com.
3 = GICS (Global Industry Classification Standard) published by Standards & Poor