HyperText Markup Language (HTML) is a type of computer language that is used to create pages that can be posted on the Internet or sent via email. Although it might seem complex to many people, it is considered to be a relatively simple language. All text, graphics, and design elements a page designed with this language are "tagged" with codes that instruct the web browser or email program how to display those elements. The tags also provide layout and formatting information so that the web page or email will look as close as possible to the way its designer intended it to look. For the novice website designer or anyone else who needs to know a certain code or wants to learn how to create an entire website, there are many software utilities, programs and websites that can assist him or her in writing HTML code.
Structure
HTML coding is structured like a tree, with each different tag nested within it. In most cases, each formatting element requires a start tag and an end tag, and different tags should not overlap. This is what is meant by "nested;" if tag 2 opens after tag 1, then tag 2 should be closed first so that the formatting element of tag 2 is entirely enclosed within tag 1. Elements are the individual components that make up the code, and include opening and closing tags and the content between them. Attributes provide more information about the element, and are made up of the attribute and its value, connected by an equal sign.
To create an HTML element, the user creates a tag that starts and finishes with angle brackets and places it before the text that needs to be formatted. The code — usually one or more letters, numbers, words, and/or symbols — inside the angle brackets indicates what the element is and the attributes that content should have, such as its size, font, or other characteristics. To end the formatting, the user types the first angle bracket, then a backslash, then repeats the element code and closes the bracket. For example, <title><strong>What Is HTML?</strong></title> is the code used to format the title of this article; the "strong" element tag is nested within the "title" tag.
Types of Codes
There are many codes to allow for different text formatting, including italics, tables, paragraphs, and hyperlinks to web pages. Codes also can indicate to the browser or email program how to display or use other elements, such as pictures, graphics, video, and sound. Other types of codes without angle brackets can be used to create punctuation marks, diacritics, and other symbols that might appear in text. Although all web browsers and many email programs use HTML, each might interpret and display the code a little differently, and designers often must consider these variations when creating a web page.
An Evolving Language
Since the development of HTML in the early 1990s by British computer scientist Tim Berners-Lee, there have been many changes and versions. These versions have been maintained by the World Wide Web Consortium (W3C) since 1996. In January 2008, the First Public Working Draft of HTML 5 was published by the working group that was developing this specification. Still under development as of 2011, this revision was expected to dramatically change application development for the web. It introduces a number of new elements, including those for site structure, interactivity, and audio and video support, as well as new attributes.
Viewing a Web Page's Code
The code used to create any web page can be seen by navigating a browser to the page, then choosing the correct option from the browser's menu. In most browsers, the user can click on the "view" menu and select an option such as "source," "view source" or "page source." This will cause a pop-up window to appear, and it will show the code that was used to create that web page.
It is important to note that not all of the content found on all web pages is written in HTML. Extensible Markup Language (XML) and Extensible HyperText Markup Language (XHTML) are other types of markup languages used in web development. In addition, style sheets — like Cascading Style Sheets (CSS) — are used to attach style to HTML documents. Languages like Flash® and Java® are used to create interactive content. Many other programming languages can be used to add specific functionality to a website.
As Compared to HTM
Practically speaking, there's little difference between HTM and HTML extensions, since both are read as an HTML file by most machines. The reason there were two different extensions to begin with is that certain types of computers, like those that ran on 16 bit DOS or Windows® 3 systems, could not read four character extensions, and so needed the three character HTM extension. Most systems that can read four character extensions are automatically programmed to recognize HTM files as HTML files, though computer users may occasionally need a converter to change a file from HTM into a format that the system recognizes.