Although I have never used Julia, this is something that is possible in Ruby, and I think this feature is seriously underrated – i.e. to be able to jump quickly to the definition of external code, modify it and run it. When you work with multiple libraries/repo this is very valuable when debugging, saves a lot of time.
It should also be possible with Node.js I think (node_modules).
It should also be possible with Node.js I think (node_modules).