SourceParameters

The source field of a field can be used to configure how that field should behave. Multiple parameters can be passed by separating them with &. For example:

id=someidhere&pfilter=somebucketfilterhere

You might notice that this looks very much like a query string and you are right. In fact the HttpUtility.ParseQueryString method is used for parsing this string.

If you want to programmatically modify the source string before passing it to the field you can take a look at the getLookupSourceItems pipeline. All fields in this repository support this pipeline.