XML stands for eXtensible Markup Language.
XML is a markup language or labels designed to structure, transport and store data, and consists of a hierarchy of brands or labels (tags) as defined by the user and can be self-descriptive of the content they carry, and also XML is the W3C.
Each user can define the name of the XML tags that are following a hierarchical structure, where each item must have the structure like this:
|<tag>||opening tag name|
|</tag>||closing tag name|
Note that the structure of all XML is hierarchical, in this case, <message> is the parent tag, the tag hanging their children, <from>, <to>, <title>, <text>.
All XML must have a label or main root, from which hang all the other labels. In the above example, the root label is <message>