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                <nav id = "navbar">
  <header>Hypertext Markup Language HTML</header>
    <a class="nav-link" href="#Introduction" rel="internal">
    <a class="nav-link" href="#History" rel="internal"><li>History</li></a>
    <a class="nav-link" href="#Markup" rel="internal"><li>Markup</li></a>
    <a class="nav-link" href="#Semantic_HTML" rel="internal"><li>Semantic HTML</li></a>
    <a class="nav-link" href="#Delivery" rel="internal"><li>Delivery</li></a>
    <a class="nav-link" href="#HTML4_Variations" rel="internal"><li>HTML4 Variations</li></a>
    <a class="nav-link" href="#HTML5_Variations" rel="internal"><li>HTML5 Variations</li></a>
    <a class="nav-link" href="#WYSIWYG_Editors" rel="internal"><li>WYSIWYG Editors</li></a>
    <a class="nav-link" href="#Reference" rel="internal"><li>Reference</li></a>
<main id = "main-page">
  <section class="main-section" id="Introduction">
      <p>Hypertext Markup Language (HTML) is the standard markup language for creating web pages and web applications. With Cascading Style Sheets (CSS) and JavaScript, it forms a triad of cornerstone technologies for the World Wide Web. <br><br>

Web browsers receive HTML documents from a web server or from local storage and render the documents into multimedia web pages. HTML describes the structure of a web page semantically and originally included cues for the appearance of the document. <br><br>

HTML elements are the building blocks of HTML pages. With HTML constructs, images and other objects such as interactive forms may be embedded into the rendered page. HTML provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items. HTML elements are delineated by tags, written using angle brackets. Tags such as <code>&lt;img /></code> and <code>&lt;input /></code> directly introduce content into the page. Other tags such as <code>&lt;p></code> surround and provide information about document text and may include other tags as sub-elements. Browsers do not display the HTML tags, but use them to interpret the content of the page. <br><br>

HTML can embed programs written in a scripting language such as JavaScript, which affects the behavior and content of web pages. Inclusion of CSS defines the look and layout of content. The World Wide Web Consortium (W3C), maintainer of both the HTML and the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1997.</p>
  <section class="main-section" id="History">
      Photograph of Tim Berners-Lee in April 2009
Tim Berners-Lee in April 2009
In 1980, physicist Tim Berners-Lee, a contractor at CERN, proposed and prototyped ENQUIRE, a system for CERN researchers to use and share documents. In 1989, Berners-Lee wrote a memo proposing an Internet-based hypertext system. Berners-Lee specified HTML and wrote the browser and server software in late 1990. That year, Berners-Lee and CERN data systems engineer Robert Cailliau collaborated on a joint request for funding, but the project was not formally adopted by CERN. In his personal notes from 1990 he listed "some of the many areas in which hypertext is used" and put an encyclopedia first. <br><br>

The first publicly available description of HTML was a document called "HTML Tags", first mentioned on the Internet by Tim Berners-Lee in late 1991. It describes 18 elements comprising the initial, relatively simple design of HTML. Except for the hyperlink tag, these were strongly influenced by SGMLguid, an in-house Standard Generalized Markup Language (SGML)-based documentation format at CERN. Eleven of these elements still exist in HTML  <br><br>

HTML is a markup language that web browsers use to interpret and compose text, images, and other material into visual or audible web pages. Default characteristics for every item of HTML markup are defined in the browser, and these characteristics can be altered or enhanced by the web page designer's additional use of CSS. Many of the text elements are found in the 1988 ISO technical report TR 9537 Techniques for using SGML, which in turn covers the features of early text formatting languages such as that used by the RUNOFF command developed in the early 1960s for the CTSS (Compatible Time-Sharing System) operating system: these formatting commands were derived from the commands used by typesetters to manually format documents. However, the SGML concept of generalized markup is based on elements (nested annotated ranges with attributes) rather than merely print effects, with also the separation of structure and markup; HTML has been progressively moved in this direction with CSS. <br><br>

Berners-Lee considered HTML to be an application of SGML. It was formally defined as such by the Internet Engineering Task Force (IETF) with the mid-1993 publication of the first proposal for an HTML specification, the "Hypertext Markup Language (HTML)" Internet Draft by Berners-Lee and Dan Connolly, which included an SGML Document type definition to define the grammar. The draft expired after six months, but was notable for its acknowledgment of the NCSA Mosaic browser's custom tag for embedding in-line images, reflecting the IETF's philosophy of basing standards on successful prototypes.[14] Similarly, Dave Raggett's competing Internet-Draft, "HTML+ (Hypertext Markup Format)", from late 1993, suggested standardizing already-implemented features like tables and fill-out forms. <br><br>

After the HTML and HTML+ drafts expired in early 1994, the IETF created an HTML Working Group, which in 1995 completed "HTML 2.0", the first HTML specification intended to be treated as a standard against which future implementations should be based. <br><br>

Further development under the auspices of the IETF was stalled by competing interests. Since 1996, the HTML specifications have been maintained, with input from commercial software vendors, by the World Wide Web Consortium (W3C). However, in 2000, HTML also became an international standard (ISO/IEC 15445:2000). HTML 4.01 was published in late 1999, with further errata published through 2001. In 2004, development began on HTML5 in the Web Hypertext Application Technology Working Group (WHATWG), which became a joint deliverable with the W3C in 2008, and completed and standardized on 28 October 2014.
   <section class="main-section" id="Markup">
      HTML markup consists of several key components, including those called tags (and their attributes), character-based data types, character references and entity references. HTML tags most commonly come in pairs like <code>&lt;h1> </code>and <code>&lt;/h1></code>, although some represent empty elements and so are unpaired, for example <code>&lt;img></code>. The first tag in such a pair is the start tag, and the second is the end tag (they are also called opening tags and closing tags). <br><br>

Another important component is the HTML document type declaration, which triggers standards mode rendering. <br><br>

The following is an example of the classic "Hello, World!" program:<br><br>

<code>&lt;!DOCTYPE html><br>
    &lt;title>This is a title&lt;/title><br>
    &lt;p>Hello world!&lt;/p><br>
      The text between <code>&lt;html></code> and <code>&lt;/html></code> describes the web page, and the text between <code>&lt;body></code> and <code>&lt;/body></code> is the visible page content. The markup text <code>&lt;title></code>This is a title <code>&lt;/title></code> defines the browser page title. <br><br>

      The Document Type Declaration <code>&lt;!DOCTYPE html></code> is for HTML5. If a declaration is not included, various browsers will revert to "quirks mode" for rendering.
      <section class="main-section" id="Semantic_HTML">
    <header>Semantic HTML</header>
      Semantic HTML is a way of writing HTML that emphasizes the meaning of the encoded information over its presentation (look). HTML has included semantic markup from its inception, but has also included presentational markup, such as <code>&lt;font></code>, <code>&lt;i></code> and <code>&lt;center></code> tags. There are also the semantically neutral span and div tags. Since the late 1990s, when Cascading Style Sheets were beginning to work in most browsers, web authors have been encouraged to avoid the use of presentational HTML markup with a view to the separation of presentation and content. <br><br>

In a 2001 discussion of the Semantic Web, Tim Berners-Lee and others gave examples of ways in which intelligent software "agents" may one day automatically crawl the web and find, filter and correlate previously unrelated, published facts for the benefit of human users. Such agents are not commonplace even now, but some of the ideas of Web 2.0, mashups and price comparison websites may be coming close. The main difference between these web application hybrids and Berners-Lee's semantic agents lies in the fact that the current aggregation and hybridization of information is usually designed in by web developers, who already know the web locations and the API semantics of the specific data they wish to mash, compare and combine. <br><br>

An important type of web agent that does crawl and read web pages automatically, without prior knowledge of what it might find, is the web crawler or search-engine spider. These software agents are dependent on the semantic clarity of web pages they find as they use various techniques and algorithms to read and index millions of web pages a day and provide web users with search facilities without which the World Wide Web's usefulness would be greatly reduced. <br><br>

In order for search-engine spiders to be able to rate the significance of pieces of text they find in HTML documents, and also for those creating mashups and other hybrids as well as for more automated agents as they are developed, the semantic structures that exist in HTML need to be widely and uniformly applied to bring out the meaning of published text. <br><br>

Presentational markup tags are deprecated in current HTML and XHTML recommendations and are illegal in HTML5. <br><br>

Good semantic HTML also improves the accessibility of web documents (see also Web Content Accessibility Guidelines). For example, when a screen reader or audio browser can correctly ascertain the structure of a document, it will not waste the visually impaired user's time by reading out repeated or irrelevant information when it has been marked up correctly.
      <section class="main-section" id="Delivery">
      HTML documents can be delivered by the same means as any other computer file. However, they are most often delivered either by HTTP from a web server or by email. <br><br>

Main article: Hypertext Transfer Protocol
The World Wide Web is composed primarily of HTML documents transmitted from web servers to web browsers using the Hypertext Transfer Protocol (HTTP). However, HTTP is used to serve images, sound, and other content, in addition to HTML. To allow the web browser to know how to handle each document it receives, other information is transmitted along with the document. This meta data usually includes the MIME type (e.g., text/html or application/xhtml+xml) and the character encoding (see Character encoding in HTML). <br><br>

In modern browsers, the MIME type that is sent with the HTML document may affect how the document is initially interpreted. A document sent with the XHTML MIME type is expected to be well-formed XML; syntax errors may cause the browser to fail to render it. The same document sent with the HTML MIME type might be displayed successfully, since some browsers are more lenient with HTML. <br><br>

The W3C recommendations state that XHTML 1.0 documents that follow guidelines set forth in the recommendation's Appendix C may be labeled with either MIME Type.[81] XHTML 1.1 also states that XHTML 1.1 documents should be labeled with either MIME type. <br><br>

      <strong>HTML e-mail</strong><br><br>
Main article: HTML email
Most graphical email clients allow the use of a subset of HTML (often ill-defined) to provide formatting and semantic markup not available with plain text. This may include typographic information like coloured headings, emphasized and quoted text, inline images and diagrams. Many such clients include both a GUI editor for composing HTML e-mail messages and a rendering engine for displaying them. Use of HTML in e-mail is criticized by some because of compatibility issues, because it can help disguise phishing attacks, because of accessibility issues for blind or visually impaired people, because it can confuse spam filters and because the message size is larger than plain text. <br><br>

      <strong>Naming conventions</strong> <br><br>
The most common filename extension for files containing HTML is .html. A common abbreviation of this is .htm, which originated because some early operating systems and file systems, such as DOS and the limitations imposed by FAT data structure, limited file extensions to three letters. <br><br>

      <strong>HTML Application</strong> <br><br>
Main article: HTML Application
An HTML Application (HTA; file extension ".hta") is a Microsoft Windows application that uses HTML and Dynamic HTML in a browser to provide the application's graphical interface. A regular HTML file is confined to the security model of the web browser's security, communicating only to web servers and manipulating only webpage objects and site cookies. An HTA runs as a fully trusted application and therefore has more privileges, like creation/editing/removal of files and Windows Registry entries. Because they operate outside the browser's security model, HTAs cannot be executed via HTTP, but must be downloaded (just like an EXE file) and executed from local file system.
      <section class="main-section" id="HTML4_Variations">
    <header>HTML4 Variations</header>
      Since its inception, HTML and its associated protocols gained acceptance relatively quickly. However, no clear standards existed in the early years of the language. Though its creators originally conceived of HTML as a semantic language devoid of presentation details, practical uses pushed many presentational elements and attributes into the language, driven largely by the various browser vendors. The latest standards surrounding HTML reflect efforts to overcome the sometimes chaotic development of the language and to create a rational foundation for building both meaningful and well-presented documents. To return HTML to its role as a semantic language, the W3C has developed style languages such as CSS and XSL to shoulder the burden of presentation. In conjunction, the HTML specification has slowly reined in the presentational elements. <br><br>

There are two axes differentiating various variations of HTML as currently specified: SGML-based HTML versus XML-based HTML (referred to as XHTML) on one axis, and strict versus transitional (loose) versus frameset on the other axis. <br><br>

      <strong>SGML-based versus XML-based HTML</strong> <br><br>
One difference in the latest HTML specifications lies in the distinction between the SGML-based specification and the XML-based specification. The XML-based specification is usually called XHTML to distinguish it clearly from the more traditional definition. However, the root element name continues to be "html" even in the XHTML-specified HTML. The W3C intended XHTML 1.0 to be identical to HTML 4.01 except where limitations of XML over the more complex SGML require workarounds. Because XHTML and HTML are closely related, they are sometimes documented in parallel. In such circumstances, some authors conflate the two names as (X)HTML or X(HTML). <br><br>

Like HTML 4.01, XHTML 1.0 has three sub-specifications: strict, transitional and frameset. <br><br>

Aside from the different opening declarations for a document, the differences between an HTML 4.01 and XHTML 1.0 document—in each of the corresponding DTDs—are largely syntactic. The underlying syntax of HTML allows many shortcuts that XHTML does not, such as elements with optional opening or closing tags, and even empty elements which must not have an end tag. By contrast, XHTML requires all elements to have an opening tag and a closing tag. XHTML, however, also introduces a new shortcut: an XHTML tag may be opened and closed within the same tag, by including a slash before the end of the tag like this: <code>&lt;br/></code>. The introduction of this shorthand, which is not used in the SGML declaration for HTML 4.01, may confuse earlier software unfamiliar with this new convention. A fix for this is to include a space before closing the tag, as such: <code>&lt;br /></code>. <br><br> 

To understand the subtle differences between HTML and XHTML, consider the transformation of a valid and well-formed XHTML 1.0 document that adheres to Appendix C (see below) into a valid HTML 4.01 document. To make this translation requires the following steps: <br><br>
<li>The language for an element should be specified with a lang attribute rather than the XHTML xml:lang attribute. XHTML uses XML's built in language-defining functionality attribute. </li>
  <li>Remove the XML namespace (xmlns=URI). HTML has no facilities for namespaces. </li>
<li>Change the document type declaration from XHTML 1.0 to HTML 4.01. (see DTD section for further explanation).</li>
<li>If present, remove the XML declaration. (Typically this is: <code>&lt;?xml version="1.0" encoding="utf-8"?></code>). </li>
<li>Ensure that the document's MIME type is set to text/html. For both HTML and XHTML, this comes from the HTTP Content-Type header sent by the server. </li>
      <li>Change the XML empty-element syntax to an HTML style empty element (<code>&lt;br /></code> to <code>&lt;br></code>). </li> <br><br>
Those are the main changes necessary to translate a document from XHTML 1.0 to HTML 4.01. To translate from HTML to XHTML would also require the addition of any omitted opening or closing tags. Whether coding in HTML or XHTML it may just be best to always include the optional tags within an HTML document rather than remembering which tags can be omitted. <br><br>

A well-formed XHTML document adheres to all the syntax requirements of XML. A valid document adheres to the content specification for XHTML, which describes the document structure. <br><br>

The W3C recommends several conventions to ensure an easy migration between HTML and XHTML (see HTML Compatibility Guidelines). The following steps can be applied to XHTML 1.0 documents only: <br><br>
  <li>Include both xml:lang and lang attributes on any elements assigning language. </li>
  <li>Use the empty-element syntax only for elements specified as empty in HTML.</li>
  <li>Include an extra space in empty-element tags: for example <code>&lt;br /></code> instead of <code>&lt;br></code>.</li>
<li>Include explicit close tags for elements that permit content but are left empty (for example, <code>&lt;div>&lt;/div></code>, not <code>&lt;div /></code>).
  <li>Omit the XML declaration.</li>
By carefully following the W3C's compatibility guidelines, a user agent should be able to interpret the document equally as HTML or XHTML. For documents that are XHTML 1.0 and have been made compatible in this way, the W3C permits them to be served either as HTML (with a text/html MIME type), or as XHTML (with an application/xhtml+xml or application/xml MIME type). When delivered as XHTML, browsers should use an XML parser, which adheres strictly to the XML specifications for parsing the document's contents. <br><br>

      <strong>Transitional versus strict</strong><br><br>
HTML 4 defined three different versions of the language: Strict, Transitional (once called Loose) and Frameset. The Strict version is intended for new documents and is considered best practice, while the Transitional and Frameset versions were developed to make it easier to transition documents that conformed to older HTML specification or didn't conform to any specification to a version of HTML 4. The Transitional and Frameset versions allow for presentational markup, which is omitted in the Strict version. Instead, cascading style sheets are encouraged to improve the presentation of HTML documents. Because XHTML 1 only defines an XML syntax for the language defined by HTML 4, the same differences apply to XHTML 1 as well. <br><br>

The Transitional version allows the following parts of the vocabulary, which are not included in the Strict version: <br><br>
  <li><strong>A looser content model</strong></li>
<li>Inline elements and plain text are allowed directly in: body, blockquote, form, noscript and noframes</li>
        <li><strong>Presentation related elements</strong><li>
          <li>underline (u)(Deprecated. can confuse a visitor with a hyperlink.)</li>
          <li>strike-through (s)</li>
          <li>center (Deprecated. use CSS instead.)</li>
          <li>font (Deprecated. use CSS instead.)</li>
          <li>basefont (Deprecated. use CSS instead.)</li>
        <li><strong>Presentation related attributes</strong></li>
<li>background (Deprecated. use CSS instead.) and bgcolor (Deprecated. use CSS instead.) attributes for body (required element according to the W3C.) element.</li>
<li>align (Deprecated. use CSS instead.) attribute on div, form, paragraph (p) and heading (h1...h6) elements</li>
<li>align (Deprecated. use CSS instead.), noshade (Deprecated. use CSS instead.), size (Deprecated. use CSS instead.) and width (Deprecated. use CSS instead.) attributes on hr element</li>
<li>align (Deprecated. use CSS instead.), border, vspace and hspace attributes on img and object (caution: the object element is only supported in Internet Explorer (from the major browsers)) elements</li>
          <li>align (Deprecated. use CSS instead.) attribute on legend and caption elements</li>
<li>align (Deprecated. use CSS instead.) and bgcolor (Deprecated. use CSS instead.) on table element</li>
<li>nowrap (Obsolete), bgcolor (Deprecated. use CSS instead.), width, height on td and th elements</li>
          <li>bgcolor (Deprecated. use CSS instead.) attribute on tr element</li>
          <li>clear (Obsolete) attribute on br element</li>
          <li>compact attribute on dl, dir and menu elements</li>
<li>type (Deprecated. use CSS instead.), compact (Deprecated. use CSS instead.) and start (Deprecated. use CSS instead.) attributes on ol and ul elements</li>
          <li>type and value attributes on li element</li>
          <li>width attribute on pre element</li>
        <li><strong>Additional elements in Transitional specification</strong></li>
<li>menu (Deprecated. use CSS instead.) list (no substitute, though unordered list is recommended)</li>
<li>dir (Deprecated. use CSS instead.) list (no substitute, though unordered list is recommended)</li>
<li>isindex (Deprecated.) (element requires server-side support and is typically added to documents server-side, form and input elements can be used as a substitute)</li>
        <li>applet (Deprecated. use the object element instead.)</li>
        <li><strong>The language (Obsolete) attribute on script element</strong> (redundant with the type attribute).</li>
        <li><strong>Frame related entities</strong></li>
<li>target (Deprecated in the map, link and form elements.) attribute on a, client-side image-map (map), link, form and base elements</li>
The Frameset version includes everything in the Transitional version, as well as the frameset element (used instead of body) and the frame element.<br><br>

      <strong>Frameset versus transitional</strong><br><br>
In addition to the above transitional differences, the frameset specifications (whether XHTML 1.0 or HTML 4.01) specify a different content model, with frameset replacing body, that contains either frame elements, or optionally noframes with a body. <br><br>

      <strong>Summary of specification versions</strong><br><br>
As this list demonstrates, the loose versions of the specification are maintained for legacy support. However, contrary to popular misconceptions, the move to XHTML does not imply a removal of this legacy support. Rather the X in XML stands for extensible and the W3C is modularizing the entire specification and opening it up to independent extensions. The primary achievement in the move from XHTML 1.0 to XHTML 1.1 is the modularization of the entire specification. The strict version of HTML is deployed in XHTML 1.1 through a set of modular extensions to the base XHTML 1.1 specification. Likewise, someone looking for the loose (transitional) or frameset specifications will find similar extended XHTML 1.1 support (much of it is contained in the legacy or frame modules). The modularization also allows for separate features to develop on their own timetable. So for example, XHTML 1.1 will allow quicker migration to emerging XML standards such as MathML (a presentational and semantic math language based on XML) and XForms—a new highly advanced web-form technology to replace the existing HTML forms. <br><br>

In summary, the HTML 4 specification primarily reined in all the various HTML implementations into a single clearly written specification based on SGML. XHTML 1.0, ported this specification, as is, to the new XML defined specification. Next, XHTML 1.1 takes advantage of the extensible nature of XML and modularizes the whole specification. XHTML 2.0 was intended to be the first step in adding new features to the specification in a standards-body-based approach.
      <section class="main-section" id="HTML5_Variations">
    <header>HTML5 Variations</header>
      <strong>WHATWG HTML versus HTML5</strong><br><br>
Main article: HTML5
The WHATWG considers their work as living standard HTML for what constitutes the state of the art in major browser implementations by Apple (Safari), Microsoft (Edge), Google (Chrome), Mozilla (Firefox), Opera (Opera), and others. HTML5 is specified by the HTML Working Group of the W3C following the W3C process. As of 2013, both specifications are similar and mostly derived from each other, i.e., the work on HTML5 started with an older WHATWG draft, and later the WHATWG living standard was based on HTML5 drafts in 2011.
      <section class="main-section" id="WYSIWYG_Editors">
    <header>WYSIWYG Editors</header>
      There are some WYSIWYG editors (What You See Is What You Get), in which the user lays out everything as it is to appear in the HTML document using a graphical user interface (GUI), often similar to word processors. The editor renders the document rather than show the code, so authors do not require extensive knowledge of HTML.<br><br>

The WYSIWYG editing model has been criticized, primarily because of the low quality of the generated code; there are voices advocating a change to the WYSIWYM model (What You See Is What You Mean).<br><br>

WYSIWYG editors remain a controversial topic because of their perceived flaws such as:<br><br>

Relying mainly on layout as opposed to meaning, often using markup that does not convey the intended meaning but simply copies the layout. <br><br>
Often producing extremely verbose and redundant code that fails to make use of the cascading nature of HTML and CSS. <br><br>
Often producing ungrammatical markup, called tag soup or semantically incorrect markup (such as <code>&lt;em></code> for italics). <br><br>
As a great deal of the information in HTML documents is not in the layout, the model has been criticized for its "what you see is all you get"-nature.
      <section class="main-section" id="Reference">
      <li>All the documentation in this page is taken from <a href=""  target="_blank">Wikipedia</a> for training purposes only


                @import url('');

    color: black;
    background-color: white;
    font-family: 'Roboto',Arial,sans-serif;
    line-height: 1.5;

  font-size: 30px;
  font-size: 30px;

  color: black;
  border:1px solid;
  list-style: none;
  color: black;
  position: absolute;
  background-color: lightgrey;