HTML 5 versus XHTML 1.0 Transitional

HTML is expressed as SGML and XHTML is expressed in XML. Creating XHTML is connected with more restrictions in the form of markup.

Avoid using the <video> or <audio> tags in XHTML 1.0 Transitional, as those are not an element of that specification.

Convert from HTML to XHTML

• Add an XHTML <!DOCTYPE> to the first line of every page
• Add a xmlns attribute to the HTML element of every page
• Change all element names to lowercase
• Close all empty elements
• Change all attribute names to lowercase
• Quote all attribute values