Why is XML so popular?

Answer
Due to the following advantages of using XML, it has become popular:

• It supports Unicode. Therefore documents written in any human language can be communicated.
• Data structures: records, lists and trees can be represented using XML.
• Its format describes structure, field names and their specific values too. Its therefore called self-documenting.
• Its syntax and parsing requirements make the necessary parsing algorithms very simple, efficient, and consistent.
• It can be used as a document storage and processing format.
• It is platform-independent.

Why is XML referred as self-describing data?

Answer
Text labels inside of XML's syntactic delimiters that cause most people to think that XML is self-describing. But these tags aren't part of XML.

Choosing the terms used for tags or naming anything is often a difficult and contentious activity. Everyone naturally creates names that make sense to them.

However, XML is not self describing.

Why is XML extensible?

Answer
Extensibility is another attribute of XML. XML is short of "eXtensible Markup Language. This is so because a developer may easily create his own XML syntax for any applications he wishes to use it for. Any other developer, once having learned how to use his own language's XML parsing routines, can use any XML-based format currently available. 

XML is a secured language for information exchange over the network. Explain

Answer
Applications require a secure exchange of structured data. XML encryption can ensure this by providing end-to-end security as it is iitself a widely used data structuring technology.

XML encryption addresses the issues not covered in by the TLS which are encrypting part of the data that is being exchanged and secure sessions between multiple parties.

XML Encryption can handle XML as well as binary data.

List the rules to be followed by an XML document.

Answer
Following rules need to be followed by an XML document:

They must have a root tag, the document should be well formed : the tags should be properly closed, since XML is case sensitive, one should take care that the documents are written with proper care and the attribute values should be inside “”