XHTML

HTML is the language of the web, and it stands for HyperText Markup Language. XHTML is almost identical, and it stands for Extensible HyperText Markup Language. The difference is that XHTML is slightly stricter and cleaner, and is defined as an XML document. XHTML is a markup language and not considered a programming language. PHP is one of the main back-end programming languages that we use, and is interpreted server-side and then delivered to the browser as XHTML.