How can MIDI tracks be included in the final mixed down wave file?

From N-Track Wiki

You can record the MIDI files to wave files, activating the MIDI out as a recording source from the soundcard's mixer or Windows volume control. Now just record a new track clicking on the record button. This newly created audio track will contain all the MIDI tracks, and you will be able to use it for the rendering. Not all soundcards can record from their MIDI out so you may have to physically connect the line out of the soundcard to its line input jack, but doing so be aware of the possible feedback problems. The latest version can do most of the work automatically with the Track/MIDI/Convert MIDI tracks to a wave tracks menu command.