What should a developer know before creating a new XML based format or language? [closed]

Question

Let's say you have to write an xml-based (no choice) language that will be some kind of "standard" format in the end, used by billions of applications around the world, or at least you hope for it. That language will be like html for internet, but in another specific domain. Something really simple and descriptive, that will be interpreted by tools and other applications.

Now let's say you have a basic understanding of how XML works (you know how tags works, that they might have attributes and that there can be elements in elements...). You really understand the domain well but you never did write a language or xml-based format specification before (other than some basic xml formats for your company internal tools).

What else do you have to know to do your job right? Maybe some XML language specific features? Maybe using a XSD file as a specification file?

To sum up : What are the best practices when designing and writing specification for this kind of language?

Answer 1

Firstly, you need to know your problem domain really, really well to make sure your markup can cover all the requirements for those billions of applications. Everything else is secondary. It's not a technology or tools issue.