sourceName: string naming a value source as it is shown on radio menus where you can select it. Notice that many names have special characters in them.
Return value
sourceIndex: integer. The source index, which can be used as input for getSourceName(sourceIndex), getValue(sourceIndex), and getFieldInfo(sourceIndex).
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 obtained here.
This function is rather time consuming, and should not be used repeatedly in a script, if it can be avoided.
Current Introduced in 2.6