HTML - HTML vs. XHTML

Overview

Estimated time: 15–25 minutes

HTML5 is the living standard and is not XML. XHTML is HTML serialized as XML, with stricter rules.

Key Differences

• Parsing: HTML is parsed as HTML; XHTML must be well-formed XML.
• Case: XHTML tags/attributes should be lowercase; HTML is case-insensitive (conventionally lowercase).
• Self-closing: XHTML uses <br />; HTML uses <br>.
• Attribute quoting: Required in XHTML; recommended in HTML.

Examples

<!-- HTML5 -->
<img src="x.png" alt="">

<!-- XHTML -->
<img src="x.png" alt="" />

Common Pitfalls

• Serving XHTML as text/html—browsers treat it as HTML, not XML.