If you want to search for packages originating from one particular software repository, use the filter. In the default configuration, this filter shows a list of all packages from the selected installation source. To restrict the list, use a secondary filter.
To view a list of the all installed packages from the selected repository, select the filter then select from list and deactivate all check boxes except .
If you are interested in the opposite and want to detect packages not belonging to any repository, also use the filter and select as the .