How do HTML and XML differ in their purposes?

1. HTML emphasizes data display and XML emphasizes the data content.
2. HTML only allow pre-defined tags and XML allow customized tags.
3. Tags in HTML are not case-sensitive and tags in XML are case-sensitive.
4. Multiple adjacent white-spaces in an element content are different from a single white-space in XML, but same in HTML
5. Double quote around attribute value are optional to HTML, but it’s compulsory in XML.
6. HTML  processed mainly by standard web browsers, and XML processed by tailor-made programs as well as generic XML parsers

Reference:
Java Application Development and Programming Languages U06, p.11, Q1