HTML 5 and XHTML 1.1

Question

I am learning HTML 5 and wondering: Can HTML 5 be used in XHTML 1.1 documents? If so, can anyone give an example?

Answer 1

Do not confuse XHTML and HTML.

XHTML is HTML, which is a valid XML document. In fact, the XHTML 1.1 standard does not apply to HTML 5, but to HTML 4.01.

What does it mean? You can select a valid XHTML 1.1 document and it will be a valid HTML 5 document, but the counterpart is not always true. For instance:

<button disabled></button> 

This is valid HTML (no matter which version), but it is not a valid XML operator (then it is not a valid XHTML document) due to an empty attribute. The world is full of these examples (only Google), HTML is very relaxed in terms of syntax (and HTML 5 has not changed this direction), and there are other differences ( here , for example). In addition, the HTML 5 standard introduced new tags that are not part of the XHTML 1.1 standard, so a fully functional HTML 5 document (despite the syntax) will not be a valid XHTML 1.1 document.

References
Here is a short list of good links to this topic, selected from SO answers:

• HTML / XHTML and MIME Type : A short answer about content type and markup syntax.
• All in one about HTML and XHTML : A long QA list that covers various aspects of HTML / XHTML compatibility.
• What to use : the question of what is best to use between HTML and XHTML (of course, the answer depends, but the answer itself is good).
• XHTML / HTML for Mobile : Some useful HTML5 / XHTML tips with Apple devices.

Answer 2

theoretically not, because the standard xhtml and html sets are different. However, if it works, it completely depends on the browser you are using, and in the most modern browser, a different set of tags will be displayed, as well as the standard that you defined.