Source filters allow for users to search for combined views without potentially creating a new one by providing keyword drop down lists that are populated only with existing keyword values.
Note:
Excessive usage of source filters can result in performing an extensive number of queries, negatively impacting performance for the user. It is recommended that you use the minimum number of keyword types a user will need to isolate a selected combined view.
You can configure the keywords you want to include in your source filter search in Combined Viewer from the Combined View Configuration page by: