Status: current Introduced in 2.6
sourceIndex: integer identifying a value source as returned by getSourceIndex(sourceName) or the id field in the table returned by getFieldInfo.
sourceName: string naming the value source as it is shown on radio menus where a source can be chosen.
The source names shown on the screen are not the same as the names used by getFieldInfo and getValue. But the indices are the same, so e.g. getValue(index) will work with the indices used here.