The term Range defines the breadth of knowledge in an industry. As software developers we often value depth of knowledge but breadth of knowledge is even more valuable in the long run.
The range of experience allows developers to think about the problem in different ways. It also allows us to makes references between different context, technologies and programming languages. As developers we must work towards maximizing our range so we can look at the problem in different ways.
Even if your primary language is not X it is always a good idea to look and learn a new language or framework because you never know what ideas you can learn from a language which can be applied at your work.