When writing your own scripts, and using some of the pre-fab tools how do you make the output load automatically into your QGIS project?

Example: In the Help Tab of the QGIS tool "saveselectedfeatures" it explains its "Console Usage" as follows:

processing.runalg('qgis:saveselectedfeatures', input_layer, output_layer)

But when you run it as its own tool from the Toolbox the GUI has you fill in the same two parameters, but also has a third: a checkbox for "Open output file after running algorithm". I checked it and it showed up as promised on my map project.

But the Tool's own HELP tab says nothing about how to script this functionality.

So how do I make the output open in the project automatically?