An in-depth explanation of the differences between HTML and XHTML

HTML (HyperText Markup Language, Hypertext Markup Language) The earliest official specification of HTML is HTML 2.0 released by IETF (Internet Engineering Task Force) in 1995. W3C (World Wide Web Consortium, World Wide Web Consortium), following the IETF, upgraded HTML several times until HTML 4.01 was released in 1999.

　HTML and XHTML

　XHTML (eXtensible HyperText Markup Language) is the first revised version of HTML 4.01. It is "reorganized from three types of HTML4 files according to the XML1.0 standard". In other words, XHTML is a hybrid of HTML 4.01 and XML1.0.

Since XHTML1.0 is based on HTML4.01, it does not introduce any new tags or attributes (XHTML can be regarded as a subset of HTML). The expression is similar to the hypertext markup language HTML, but the syntax is more strict, almost All web browsers are compatible with XHTML while correctly parsing HTML.

　For example: all tags in XHTML must be lowercase, all tags must be closed, and every attribute must be enclosed in quotation marks.
should be written as
, not
(same as hr); after using

, there must be a

to end the paragraph.

　HTML and XML

　HTML is an application based on Standard Generalized Markup Language (SGML), while XHTML is based on Extensible Markup Language (XML). HTML and XHTML are actually two standards that developed in parallel. In essence, XHTML is a transitional technology that combines some of the powerful features of XML with most of the simple features of HTML. The purpose of establishing XHTML is to realize the transition from HTML to XML.

　 XML is designed to transmit and carry data information, not to represent or display data. HTML language is used to represent data. RSS and ATOM have now become successful XML applications. RSS uses XML as a standard way to share content with each other. It stands for Really Simple Syndication (or RDF Site Summary, RDF site summary). It makes it easy for others to discover that you have updated your site. There seem to be fewer Atom data sources; for developers, RSS is relatively simple, and Atom is a little more complicated, especially if you are not familiar with XML.

　In 1997, when W3C released the XML1.0 standard, HTML version had already reached version 4. Until January 26, 2000, XHTML1.0 became a W3C recommended standard. However, in view of the current situation of HTML dominating the world at that time, W3C had no choice but to recommend "continuing to use HTML4.01 and actively research plans for HTML5 and XHTML." In 2002, W3C pointed out that the XHTML family would be a new stage of the Internet, and began to develop XHTML2, aiming to lead the Web to an extremely bright future based on XML.

　HTML5 is popular

Since XHTML originally only improved the original HTML system in terms of content structure, XHTML2.0 only paid more attention to page specifications and usability based on XHTML1.1, and lacked interactivity. In this era when Web Apps are popular, XHTML2 is somewhat out of date, so HTML5 was born.

　The W3C ignores the needs of web designers and works behind closed doors from a theoretical perspective. However, it carries the banner of standards, triggering opposition from browser manufacturers such as Opera, Apple, and Mozilla. In 2004, they formed an organization with the purpose of promoting the HTML5 standard for the Internet - the Web Hypertext Application Technology Working Group (WHATWG).

　Competition between HTML5 and XHTML2

　HTML5 aims to replace the HTML4.01 and XHTML1.0 standards formulated in 1999, aiming to improve web page performance and increase page interaction. HTML5 has absorbed some suggestions from XHTML2, including some features to improve document structure. For example, the use of new HTML tags header, footer, dialog, aside, figure, etc. will allow content creators to create documents more semantically. Previous development Readers always use div in these situations.

　After years of hard work, W3C and WHATWG finally reached a compromise in 2006. In October 2006, Tim Berners-Lee, the father of the Web, chairman of the World Wide Web Consortium (W3C), and member of the National Academy of Sciences, published a blog post stating that the path from HTML to XML is OK. It doesn't make sense (XHTML is dead). In 2009, W3C wisely gave up the plan to improve the XHTML2.0 standard and chose the results of WHATWG as the basis. In fact, XHTML was not modified in the years after it was updated in 2002, although many problems were discovered.

In 2011, Ian Hickson, a Google engineer and HTML5 standard editor, said that HTML5 will be the last HTML language with a version number. He said that the HTML language will become a living standard.