How to create combined workplace.dsl file like in big-bank-plc example?

[jimaldon]

Question

I like how workplace.dsl files are broken up according to software system containers of internetbankingsystem and systemlandscape here

however a render tool will only accept 1 workplace.dsl file, like the one in the root above. How was that file created? Is there a tool to work with multiple workplace.dsl files that refer to each other?