XHTML and HTML are both markup languages, but their use cases are different. This common senior web designer interview question is answered below.  XHTML: Extensible Hypertext Markup Language is what XHTML refers to. Since XHTML combines elements from both XML and HTML, it may be thought of as a subset of XML. When you combine XML with HTML, you get XHTML. XHTML is often seen as an enhanced form of HTML.  HTML: Hypertext Markup Language (HTML) is the most used language on the web. Websites and their interconnectivity are made possible using HTML. Just so we're clear, HTML is a markup language and not a programming language. HTML sites may be given a fresh design with the help of additional technologies like CSS and JavaScript.  XHTML HTML Extensible Hypertext Markup Language is what it means with XHTML. Hypertext Markup Language is the acronym for HTML. The World Wide Web Consortium, or W3C, created it. Tim Berners-Lee has developed it. Originating with XML and HTML, it has undergone expansion. It is an augmentation of SGML (Standard Generalized Markup Language). It's a markup language, the format's defining characteristic. This is a document data format. It is necessary to include a doctype declaration at the beginning of your file. You do not need to write the doctype at the top. Throughout this, all tags and attributes must be written in lowercase. No strict case sensitivity is required for tags or attributes. It is required that quotations be cited when utilizing the attributes. It is not required to include quotes when using the attributes. The tags must be closed in the same sequence in which they were opened. Tags need not be closed in the same sequence in which they were opened. The .xhtml, .xht, and .xml filename extensions are supported. The .html and .htm file extensions are often used.