Understanding HTML, XHTML, and HTML5

• ·        HTML is an acronym for Hypertext Markup Language, which is the language we have used to create webpages since the first webpages arrived on the web.
• ·        HTML roots are from an older markup language that was used in document publishing, called SGML (Standard Generalized Markup Language).
• ·        Like SGML, HTML uses tags to provide formatting features such as <b>this is bold</b>, which would cause the text within the starting b tag and ending b tag to render as bolded text.
• ·        Notice the difference between the first and second tag; the second tag has a slash (/) to indicate that it’s an ending tag. Many but not all HTML tags have a matching end tag.
• ·        HTML tags such as <br> and <img> did not have ending tags because the <br> just rendered a line break, and the <img> tag just rendered an image.
• ·        One interesting aspect of HTML and its relationship with browsers was that browsers were designed to be backward compatible and forward compatible. Creating a browser that is backward compatible is relatively easy because the problem domain is known, but how is forward compatibility accomplished? Browsers were created to ignore tags that they didn’t recognize.
• ·        For example, if a browser came across a <xyz> tag that it didn’t recognize, it would skip over the tag as though it didn’t exist. Although HTML served its purpose for quite some time, people wanted more.
• ·        Another evolving technology, called XML (eXtensible Markup Language), was becoming popular.
• ·        XML looks a lot like HTML because both languages use tags. However, there are several big differences.
• ·        First, XML always requires matching end tags for every tag, although you can use a shortcut notation to denote a starting tag and ending tag together.
• ·        Another difference is that HTML has a very specific set of tag names, and each of these tags denotes a formatting feature that is to be applied to the rendered webpage.
• ·        XML doesn’t have a defined set of tag names, so you create your own tag names, and the tags can represent anything.
• ·        XML tags are typically metadata tags: tags that describe the data that is within the tag. Although there are many other differences, one other large difference is that XML uses XML Schema Definition (XSD) technology, which validates the format of an XML document to ensure that all aspects of a document are valid before processing the XML document.
• ·        HTML’s lack of rigid structure prevented the creation of a technology such as XSD that could validate HTML documents.
• ·        The World Wide Web Consortium, also known as W3C (http://ww.w3c.org), is responsible for developing open standards for the web. The W3C introduced XHTML to solve the problems in HTML, which was up to version 4.
• ·        XHTML is an XML-based specification that tightened the HTML specification to make HTML adhere to the XML rules that describe a well-formed document, such as having a matching end tag for each starting tag.
• ·        This meant that XHTML documents could be validated by using XSD files and could be edited by using XML tools.
• ·        Although XHTML solved some problems, other problems still needed a solution. There was a need for an increasing amount of multimedia on the web. Companies wanted the flashiest (pun intended) website.
• ·        Cascading Style Sheets (CSS) provided support for adding styles such as colors and fonts consistently across a website, but companies wanted more. They wanted their webpages to be highly interactive, with video and animations.
• ·        Browsers added programmable support bzy providing JavaScript, but early versions of JavaScript were slow and difficult to program.
• ·        The browsers became extensible by providing an application programming interface (API) that would allow third parties to create plug-ins that could run in the browser’s environment. One such plug-in is Flash, which has a very large installed base.
• ·        Flash provides a development environment that can be used to create a rich user experience. Although third-party plug-ins solved the immediate need for technology to create flashy websites, there was still a need for tighter integration of multimedia with the browser, especially on small devices.
• ·        HTML5 does not originate from XHTML; HTML5 originates from HTML 4.01. As a rule, however, applying XHTML rules to your HTML5 will make your webpage more compliant with a wider variety of browsers and webpage readers, generators, and validators.
• ·        HTML5 represents a reinvented HTML, CSS, and JavaScript in a way that solves the need for rich, interactive websites that can play audio and video and support animations from within the browser without the need for plug-ins. HTML5 contains most of the tags from HTML 4.01, but many of the tags have been redefined to be semantic tags.