What does “XML” stand for? If it just stands for “Extensible Markup Language.” The name emphasizes the key feature of the language as it will be seen by an HTML user - the ability to define your own tags and attributes, which, of course, HTML does not allow. So XML is just HTML on steroids? And why PHP and XML can be connected together, like PHP XML scripts? What’s the relation between them.
HTML is one descendant of SGML (Structured General Markup Language) and XML is another. XHTML, which you may have also heard of, is HTML written in XML. MathML is a way to encode mathematical equations using XML.
Basically, XML is a language for making languages.
PHP is an interpreted programming language, like Ruby or Perl or Tcl, and it runs on the Web server using either the command-line, CGI, or an Apache module called mod_php. It can be used to write nearly any sort of application you might need. Along the way, it inherits a lot of Perl’s text-manipulation prowess, which allows it to generate text-based output like (wait for it) XML. There are also some modules in PHP which allow it to directly manipulate XML using the Saxon parser and XSLT.
But saying that PHP and XML go together ignores the fact that PHP and HTML or PHP and MySQL or PHP and Regular Expressions, or PHP and name any other programming technology – all go together. They’re orthogonal, to use the library science term.