Due to the behaviour of people in the past, access to the source code online has been restricted. On the other hand access to online source code is very impractical. Anyway, it is possible to get the full core of the game (the core of the game does not refer to modules) from the repositories. You may download the entirety of the latest publically released stable version from:
Original version of core: DragonPrime Fork with improves: IDMarinas Edition (It's this version you're looking at.)
You may then work with that code within the restrictions of its license.
Hopefully this will help put an end to actions like the following:
Releasing code which they do not own without permission.
Removing valid copyright information from code and replacing it.
Removing portions of the code required to be kept intact by licensing.
Claiming copyright of items which they did not create.