What is Xml?

Question

what is xml?
what is its function?
how can I learn it?(website,android apk,...)

Answer 1

1) XML (eXtensive Markup Langauge) is a markup language similar to HTML syntax wise but has no predefined tags (<div>, <p> ect) and has stricter syntax rules than HTML
2) Unlike HTML, XML is not used to display things but rather just store data using author defined tags e.g.
<user>
<name> John Smith </name>
<age> 28 </age>
</user>
3) https://www.w3schools.com/xml/xml_whatis.asp

Answer 2

If you know HTML, you pretty much already know XML. All you need is that XML declaration thingy, knowing how to save text files as .xml and knowing that you decide all of the tag names.