XML Course

XML (eXtensible Markup Language) is a markup language for storing and transporting data using tags you invent yourself, rather than a fixed set like HTML's. It shows up less on the visible web today than it used to, but it's still underneath a surprising amount of what you use daily — Word and Excel files, RSS feeds, Android layout files, and a long list of enterprise data formats.

What you'll learn

You'll start with what makes XML different from HTML — self-describing tags, strict structural rules, and a document that either parses cleanly or doesn't parse at all. From there the course covers the rules that make a document "well-formed," how DTDs describe what a valid document is allowed to contain, how namespaces let you safely combine vocabularies from different sources, and how to query a document with XPath. The final lesson is an honest comparison of XML against JSON, and where each one actually gets used today.

Lessons

  1. Introduction
  2. Elements & Attributes
  3. Document Structure
  4. Well-Formedness Rules
  5. DTDs
  6. XML Namespaces
  7. XPath Basics
  8. XML vs JSON
Where to start: begin with Introduction and go in order. If you've already worked through the HTML course, several ideas here will feel familiar — but XML's rules are noticeably stricter, and lesson 4 (Well-Formedness Rules) explains exactly why.