XML vs HTML: Key Differences Every Developer Must Know
XML is a meta-language for defining custom data structures; HTML is a fixed vocabulary for describing web pages.
People confuse them because both use angle-brackets and nesting, but XML is about carrying any data, while HTML is about presenting that data in browsers.
Key Differences
XML is extensible—tags are invented by the author—while HTML’s tags are predefined by the WHATWG spec. XML is case-sensitive; HTML is not. XML focuses on structure, HTML on display.
Which One Should You Choose?
Need data exchange, config files, or APIs? Pick XML. Building web pages or apps? Stick with HTML. Many projects combine both: XML for data, HTML for rendering.
Can I embed XML inside HTML?
Yes, via script tags or XML islands, but browsers only render HTML elements.
Is HTML just a subset of XML?
Only XHTML is; modern HTML5 is no longer required to be well-formed XML.
Do search engines prefer one?
Search engines index HTML directly; XML sitemaps help them discover the HTML pages faster.