HTML and XHTML online resources

References and Specifications

• HTML 4.01 Specification
• XHTML 1.0 Specification
• XHTML 1.1 Recommendation
• HTML 4.01 Reference by W3Schools
• XHTML 1.0 Reference by W3Schools

Guides and Tutorials

• HTML Tutorial by W3Schools
• XHTML Tutorial by W3Schools

Other Resources

• W3 MarkUp Validation Service