Following this answer's suggestion, I attempted to use the "Import Plug-ins and Fragments" feature to import into my project other plugin's source code:
But the fact is, it doesn't seem to show up any source folders, as I'd expect:
Am I doing something wrong?
I suspect that your active target platform does not contain the sources. If you use your running Eclipse installation as target platform, you might want to install an Eclipse package containing sources, for example Eclipse Classic or Eclipse for RCP and RAP developers.
