What is the World Wide Web?
The World Wide Web (Web) is a network of information resources. The Web relies on three mechanisms to make these resources readily available to the widest possible audience:
- A uniform naming scheme for locating resources on the Web (e.g., URIs).
- Protocols, for access to named resources over the Web (e.g., HTTP).
- Hypertext, for easy navigation among resources (e.g., HTML).
What is HTML?
HTML, which stands for HyperText Markup Language, is the predominant markup language for web pages. It provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items. It allows images and objects to be embedded and can be used to create interactive forms. It is written in the form of HTML elements consisting of "tags" surrounded by angle brackets within the web page content. It can embed scripts in languages such as JavaScript which affect the behavior of HTML webpages. HTML can also be used to include Cascading Style Sheets (CSS) to define the appearance and layout of text and other material. The W3C, maintainer of both HTML and CSS standards, encourages the use of CSS over explicit presentational markup.’
HTML is the hyper text markup language used to design and create webpages. HTML elements are the fundamentals of HTML. A HTML document is simply a text file make up of HTML elements. These elements are defined as using HTML tags. HTML tags tell your web browser which elements to present and how to present them. The order in which the tags appear determines where the element will appear.
Markup
HTML markup consists of several key components, including elements (and their attributes), character-based data types, character references and entity references. Another important component is the document type declaration, which specifies the Document Type Definition.
The Hello world program, a common computer program employed for comparing programming languages, scripting languages and markup languages is made of 9 lines of code in HTML, albeit Newlines are optional:
<!doctype html>
<html>
<head>
<title>Hello HTML</title>
</head>
<body>
<p>Hello World!</p>
</body>
</html>
An HTML element is an individual component of an HTML document. HTML documents are composed of a tree of HTML elements and other nodes, such as text nodes. Each element can have attributes specified. Elements can also have content, including other elements and text. HTML elements represent semantics, or meaning. For example, the title element represents the title of the document.
In the HTML syntax, most elements are written with a start tag and an end tag, with the content in between. Tags are composed of the name of the element, surrounded by angle brackets. An end tag also has a slash after the opening angle bracket, to distinguish it from the start tag. For example, a paragraph, which is represented by the p element, would be written as<p>In the HTML syntax, most elements are written ...</p>
Document structure elements
<html>...</html>
The Root element of an HTML document; all other elements are contained in this.
The HTML element delimits the beginning and the end of an HTML document.
<head>...</head>
Container for processing information and metadata for an HTML document.
(See Document head elements for child elements.)
<body>...</body>
Container for the displayable content of an HTML document.
(See Document body elements for child elements.)
[edit] Document head elements
<base>
Specifies a base URL for all relative href and other links in the document. Must appear before any element that refers to an external resource. HTML permits only one base element for each document. The base element has attributes, but no contents.
.
<link>
Specifies links to other documents, such as previous and next links, or alternate versions.[7] A common use is to link to external stylesheets, using the form:
<link rel="stylesheet" type="text/css" href="url" title="description_of_style">[8]
A less-common, but important, usage is to supply navigation hints consistently through use of microformats. Several common relationships are defined, that may be exposed to users through the browser interface rather than directly in the web page.
<link rel="next" href="url">
A document’s head element may contain any number of link elements. The link element has attributes, but no contents.
<meta>
Can be used to specify additional metadata about a document, such as its author, publication date, expiration date, page description, keywords, or other information not provided through the other header elements and attributes. Because of their generic nature, meta elements specify associative key-value pairs.
In one form, meta elements can specify HTTP headers which should be sent by a web server before the actual content, for example:
<meta http-equiv="foo" content="bar">
— this specifies that the page should be served with an HTTP header called foo that has a value bar.
In the general form, a meta element specifies name and associated content attributes describing aspects of the HTML page. To prevent possible ambiguity, an optional third attribute, scheme, may be supplied to specify a semantic framework that defines the meaning of the key and its value: for example:
<meta name="foo" content="bar" scheme="DC">
In this example, the meta element identifies itself as containing the foo element, with a value of bar, from the DC or Dublin Core resource description framework.
<object>…</object>
Used for including generic objects within the document header. Though rarely used within a head element, it could potentially be used to extract foreign data and associate it with the current document.
<script>…</script>
Can act as a container for script instructions or link to an external script with the optional src attribute.[9] Also usable in the document body to dynamically generate either both block or inline content.
<style>…</style>
Specifies a style for the document, usually in the form:
<style type="text/css"> … </style>
Can either act as a container for style instructions or link to external stylesheets – for example, in CSS, with @import directives of the form:
<style> @import url; </style>[10]
<title>…</title>
Define a document title. Required in every HTML and XHTML document. User agents may use the title in different ways. For example:
· Web browsers usually display it in a window’s title bar when the window is open, and (where applicable) in the task bar when the window is minimized.
· It may become the default filename when saving the page.
· Search engines’ web crawlers may pay particular attention to the words used in the title.
The title element must not contain other elements, only text. Only one title element is permitted in a document.
[edit] Document body elements
In visual browsers, displayable elements can be rendered as either block or inline. While all elements are part of the document sequence, block elements appear within their parent elements:
- as rectangular objects which do not break across lines;
- with block margins, width and height properties which can be set independently of the surrounding elements.
Conversely, inline elements are treated as part of the flow of document text; they cannot have margins, width or height set, and do break across lines.
[edit] Block elements
[edit] Basic text
<p>…</p>
Creates a paragraph, perhaps the most common block level element.
<h1>…</h1> <h2>…</h2> <h3>…</h3> <h4>…</h4> <h5>…</h5> <h6>…</h6>
Section headings at different levels. <h1> delimits the highest-level heading, <h2> the next level down (sub-section), <h3> for a level below that, and so on to <h6>.
Most visual browsers show headings as large bold text by default, though this can be overridden with CSS. Heading elements are not intended merely for creating large or bold text — they describe the document’s structure and organization. Some programs use them to generate outlines and tables of contents.
<dl>…</dl>
A definition list (consisting of definition terms paired with definitions).
<dt>…</dt>
A definition term in a definition list.
<dd>…</dd>
The definition of a term, in a definition list.
<ol>…</ol>
An ordered (enumerated) list. The type attribute can be used to specify the kind of ordering, but stylesheets give more control: {list-style-type: foo}. The default is Arabic numbering.
<ul>…</ul>
An unordered (bulleted) list. Stylesheets can be used to specify the list marker: {list-style-type: foo}. The default marker is a disc.
<li>…</li>
A list item in ordered (ol) or unordered (ul) lists.
[edit] Other block elements
<address>…</address>
Contact information for the document author.
<blockquote>…</blockquote>
A block-level quotation, for when the quotation includes block level elements, e.g. paragraphs. The cite attribute may give the source, and must be a fully qualified Uniform Resource Identifier.
The default presentation of block quotations in visual browsers is usually to indent them from both margins. This has led to the element being unnecessarily used just to indent paragraphs, regardless of semantics. For quotations not containing block level elements see the quote (q) element.
<del>...</del>
Marks a deleted section of content. This element can also be used as inline.
<div>…</div>
Main article: Span and div
A block-level logical division. A generic element with no semantic meaning used to distinguish a document section, usually for purposes such as presentation or behaviour controlled by stylesheets or DOM calls.
<hr>
A horizontal rule. Presentational rules can also be drawn with stylesheets.
<ins>...</ins>
Marks a section of inserted content. This element can also be used as inline.
<noscript>...</noscript>
Replacement content for scripts. Unlike script this can only be used as a block-level element.
<pre>…</pre>
Pre-formatted text. Text within this element is typically displayed in a non-proportional font exactly as it is laid out in the file (see ASCII art). Whereas browsers ignore whitespace for other HTML elements, in pre, whitespace should be rendered as authored. (With the CSS properties: {white-space: pre; font-family: monospace;}, other elements can be presented in the same way.) This element can contain any inline element except: image (IMG), object (OBJECT), big font size (BIG), small font size (SMALL), superscript (SUP), and subscript (SUB).
PRE existed in HTML Internet Draft 1.2, and was standardised in HTML 2.0; still current.
<script>...</script>
Places a script in the document. Also usable in the head and in inline contexts.
Note: SCRIPT is not itself either a block or inline element; by itself it should not display at all, but it can contain instructions to dynamically generate either both block or inline content.
.
[edit] Inline elements
Inline elements cannot be placed directly inside the body element; they must be wholly nested within block-level elements [11].
[edit] Anchor
<a>…</a>
An anchor element is called an anchor because web designers can use it to anchor a URL to some text on a web page. When users view the web page in a browser, they can click the text to activate the link and visit the page whose URL is in the link.[12]
In HTML, an anchor can be either the origin or the target (destination) end of a hyperlink.
With the attribute href (hypertext reference [1]), the anchor becomes a hyperlink to either another part of the document or another resource (e.g. a webpage) using an external URL.
Alternatively (and sometimes concurrently), with the name or id attributes set, the element becomes a target. A Uniform Resource Locator can link to this target via a fragment identifier. Any element can now be made into an anchor by using the id attribute,[2] so using <a name="foo"> is not necessary.
The attribute title may be set to give brief information about the link:
<a href="URL" title="additional information">link text</a>
In most graphical browsers, when the cursor hovers over a link, it typically changes into a hand with a stretched index finger, and the title appears in some way (varies according to browser). Some browsers render alt text the same way, though this is technically incorrect.
[edit] Phrase elements
[edit] General
<abbr>…</abbr>
Marks an abbreviation, and can make the full form available:
<abbr title="abbreviation">abbr.</abbr>
<acronym>…</acronym>
Similar to the abbr element, but marks an acronym:
<acronym title="Hyper-Text Markup Language">HTML</acronym>
<dfn>…</dfn>
Inline definition of a single term.
<em>…</em>
Emphasis (conventionally displayed in italics)
<strong>…</strong>
strong emphasis (conventionally displayed bold).
An aural user agent may use different voices for emphasis.
[edit] Computer phrase elements
These elements are useful primarily for documenting computer code development and user interaction through differentiation of source code (<code>), source code variables (<var>), user input (<kbd>), and terminal output (<samp>).
<code>…</code>
A code snippet. Conventionally rendered in a monospace font: Code snippet.
<samp>…</samp>
Sample output (from a program or script)
<kbd>…</kbd>
Keyboard - text to be entered by the user
<var>…</var>
Variable
[edit] Presentation
As visual presentational markup only applies directly to visual browsers, its use is discouraged. Stylesheets should be used instead. Several of these elements are deprecated or invalid in HTML 4 / XHTML 1.0, and the remainder are invalid in the current draft of XHTML 2.0. The current draft of HTML 5, however, includes <b>, <i>, and <small>.
<b>…</b>
Sets font to boldface where possible. (Equivalent CSS: {font-weight: bold}.) <strong>...</strong> usually has the same effect in visual browsers, as well as having more semantic meaning.
<i>…</i>
Sets font to italic where possible. (Equivalent CSS: {font-style: italic}.) <em>...</em> usually has the same effect in visual browsers, as well as having more semantic meaning.
<big>…</big>
Increases font size (bigger text). Equivalent CSS: {font-size: larger}
<small>…</small>
Decreases font size (smaller text). Equivalent CSS: {font-size: smaller}
.
<tt>…</tt>
Fixed-width font (typewriter-like), also known as teletype. (Equivalent CSS: {font-family: monospace;})
TT existed in HTML Internet Draft 1.2, and was standardised in HTML 2.0; still current.
<font>…</font> (deprecated)
<font [color=color] [size=size] [face=face]>…</font>
Can specify the font color with the color attribute, typeface with the face attribute, and absolute or relative size with the size attribute.
Examples (all uses are deprecated, use CSS equivalents if possible):
1. <font color="green">text</font> creates green text.
2. <font color="#114499">text</font> creates text with hexadecimal color #114499.
3. <font size="4">text</font> creates text with size 4. Sizes are from 1 to 7. The standard size is 3, unless otherwise specified in the <body> or other tags.
4. <font size="+1">text</font> creates text with size 1 bigger than the standard. <font size="-1">text</font> is opposite.
5. <font face="Courier">text</font> makes text with Courier font.
Equivalent CSS for font attributes:
· <font size="N"> corresponds to {font-size: Yunits} (the HTML specification does not define the relationship between size N and unit-size Y, nor does it define a unit).
· <font color="red"> corresponds to {color: red}
· <font face="Courier"> corresponds to {font-family: "Courier"}
<span>…</span>
Main article: Span and div
An inline logical division. A generic element with no semantic meaning used to distinguish a document section, usually for purposes such as presentation or behaviour controlled by stylesheets or DOM calls.
[edit] Other inline elements
<br>
A forced line-break.
<bdo>…</bdo>
Marks an inline section of text in which the reading direction is the opposite from that of the parent element.
<cite>…</cite>
A citation. Reference for a quote or statement in the document.
<del>…</del>
Deleted text. Typically rendered as a strikethrough: Deleted text.
<ins>…</ins>
Inserted text. Often used to mark up replacement text for <del>'d text. Typically rendered underlined: Inserted text.
Note, both <ins> and <del> elements may also be used as block elements: containing other block and inline elements. However, these elements must still remain wholly within their parent element to maintain a well-formed HTML document. For example deleting text from the middle of one paragraph across several other paragraphs and ending in a final paragraph would need to use three separate <del> elements. Two <del> elements would be required as inline element to indicate the deletion of text in the first and last paragraphs, and a third, used as a block element, to indicate the deletion in the intervening paragraphs.
<q>…</q>
An inline quotation (for block level quotation see BLOCKQUOTE). Quote elements may be nested.
<q> should automatically generate quotation marks in conjunction with Stylesheets. Practical concerns due to browser non-compliance may force authors to find work-arounds.
The cite attribute gives the source, and must be a fully qualified URI.
Note: Lengthy inline quotations may be displayed as indented blocks (as blockquote) using stylesheets. For example, with a suitable CSS rule associated with q.lengthy:
<q class="lengthy">An inline quotation of significant length (say 25 words, for example) goes here...</q>
<script>...</script>
Places a script in the document. Also usable in the head and in block contexts.
Note: <script> is not itself either a block or inline element; by itself it should not display at all, but it can contain instructions to dynamically generate either both block or inline content.
<sub>…</sub> and <sup>…</sup>
Mark subscript or superscript text. (Equivalent CSS: {vertical-align: sub} or {vertical-align: super}.)
Both were proposed in the HTML 3.0 Drafts; Standardised in HTML 3.2; still current.
[edit] Images and objects
<area>
Specifies a focusable area in a map.
<img>
Used by visual user agents to insert an image in the document. The src attribute specifies the image URL. The required alt attribute provides alternative text in case the image cannot be displayed.[13] (Though alt is intended as alternative text, Microsoft Internet Explorer renders it as a tooltip if no title is given. Safari and Google Chrome, on the other hand, do not display the alt attribute at all.)[14] img was proposed by Marc Andreessen and implemented in the NSCA Mosaic web browser.[15]
IMG existed in HTML Internet Draft 1.2, and was standardised in HTML 2.0; still current.
<map>…</map>
Specifies a client-side image map.
<object>…</object>
Includes an object in the page of the type specified by the type attribute. This may be in any MIME-type the user agent understands, such as an embedded HTML page, a file to be handled by a plug-in such as Flash, a Java applet, a sound file, etc.
<param>
Originally introduced with applet, this element is now used with, and should only occur as a child of object. It uses attributes to set a parameter for the object, e.g. width, height, font, background colour, etc., depending on the type of object. An object can have multiple params.
These are just a few of the many HTML tags and elements that are available to the novice or experienced web developer to use to develop and design web pages or websites. For a complete list of elements and attributes, follow these links to the World Wide Web Consortium.
http://www.w3.org/TR/html401/index/elements.html
http://www.w3.org/TR/html401/index/attributes.html