When is xml used?

Question

HTML

When do I use xml ?
expandable is understandable, but why xml when there is html?
in what cases would you use xml?

Answer 1

but why xml when there is html ?

xml is not like html, xml is like json.
For data transfer, not for output.

Answer 2

You are all confused.
xml is simply an ordered data format that is used to convey structured data.
HTML Markup Language
In other words, XML is an idea, HTML is one of the concrete implementations.
For example, there is fb2 - an e-book format that uses XML to separate chapters, cover, author, book title, etc.
The modern office uses DOCX and XLSX - which also use XML as their data format.