What Is HyperText Markup Language?
The HyperText Markup Language (HTML) is a language used to describe the structure of hypertext documents available on the World Wide Web that is on the Internet. All websites are written in HTML code that is read and processed by the browser, which generates the page that is displayed on the computer screen.
HTML is not a programming language but a markup language, which describes the content, textual or otherwise, of a web page. Point HTML (.html) or point HTM (.htm) is also the common extension of HTML documents.
HTML is a language whose syntax is public domain established by the World Wide Web Consortium (W3C), which is based on another language with more general purposes, the SGML.
It was developed in the late eighties by Tim Berners-Lee at CERN in Geneva. By 1994 he had a strong diffusion, following the first commercial use of the Web. Over the years, following the development of Internet, HTML has undergone many revisions, extensions and improvements, which were listed according to the classic numbering used to describe the versions of the software.
Currently the latest version available is version 4.01, released on 24 December 1999. After a period of suspension, in which the W3C has focused primarily on the definitions of XHTML (application of rules to HTML and XML-style syntax) and stylesheets (Cascading Style Sheet, CSS) in 2007 and repeat the activity specification with the definition, still in progress, HTML 5 is currently in draft status (draft).
An additional and important feature of HTML is that it was designed to define the logical content and not the final appearance of the document. Devices that can access an HTML document are varied and not always equipped with powerful graphics capabilities.
Precisely for this reason the developers have opted for the HTML language that describes the logical point of view, rather than graphical content of documents. This means that there is no guarantee that the same document to appear in the same way on two devices. While this has imposed in the past severely limited by the developers of Web pages, has secured the second highest Internet penetration and avoid it becoming a medium for elites.
Currently HTML documents are able to incorporate many technologies, which offer the possibility to add controls to the hypertext document on the yield more sophisticated graphics, dynamic interactions with the user, interactive animation and multimedia content. These languages are CSS, JavaScript or Java, and are used chiefly for multimedia applications, vector animation or streaming audio or video.
Nowadays many designers delegate writing the HTML code to specific applications, such as the so-called WYSIWYG editor that allows the designer to handle the graphic end of the page and the actual code is generated automatically. The developers prefer instead to use the HTML code directly, so you have more control over the final result and the cleaning of the written code, which the WYSIWYG editor today despite more and more advanced they can not always guarantee.
Access via the Internet
HTML documents are typically stored on hard drives (server) machine that was connected to the Internet. On these machines you have installed a software called Web server, which is responsible to produce and send documents to the browsers of users who request the transfer using the HTTP protocol.
Often, the HTML document is generated wholly or partly by a resident executable code on the Internet server capable of interacting with other applications on the server itself, such as a database, and then send the browser the end result, creating the so-called dynamic pages with which a user can perform advanced interactive operations (for example, filter the articles in an online catalog). Is the case of documents written in languages such as ASP, PHP or Perl.
Syntactical elements
Each hypertext document written in HTML must be contained in a file whose extension is typically.htm or.html.
The main component of the syntax of this language is the element, understood as a basic structure to which is delegated the function to format the data or information to indicate to the browser.
Each element is enclosed within these markings, tags, consisting of a sequence of characters enclosed between two angle brackets, i.e., the major and minor marks (Example: <br>; tag this example serves to indicate a carriage return).
When the tag should be applied to a section of text or code, the scope should be defined between an opening tag and closing (closing explicit), which coincides with the start tag preceded by a slash (/) after the opening angle bracket (Example: <b> text text text </ b>. In this case the text between these two tags will appear bold by the browser).
Some tags have an application on time, such as the tag <img> used to insert an image at a given point on the page, and as such do not require a closing tag, in which case there is talk of closing tag implied. In XHTML, however, the Implicit closing is forbidden and all tags must always be explicitly closed by a closing tag or in the case of the tags on time, using the character ‘/’ at the end of the tag itself (for example <br /> ). For these tags, browsers are able to accept both modes, for compatibility reasons.
Structure of an HTML document
An HTML document begins by stating the definition of the type of document (Document Type Definition or DTD), which tells the browser the URL of the HTML specification used for the document, indicating thus implicitly as elements, attributes and entities can use and what version of HTML is being referenced. Indeed, this information serves to the browser to identify the rules of interpretation and display appropriate for the specific document. This definition should therefore precede all the tags on the document itself.
After the DTD, the HTML document presents a nested tree structure, consisting of sections bounded by descriptive tags in them that contain even smaller subsections, again bounded by tags.
The outer structure is the one that defines the entire document, except for the DTD, and is between <html> and </ html>.
Within <html> the standard has always included the definition of two distinct sections and arranged in orderly sequence:
- The section header or header, bounded between the <head> and </ head>, which contains control information not normally displayed by the browser, with the exception of some elements
- The section of the body or body, lined in the HTML body and </ body>, which contains the information itself, ie text, images and links that constitute the part displayed by the browser.
Beneath this general division, the standard does not provide specific requirements regarding the order and placement of additional subsections within the header or body, other than an indication of respect for properly nested (sub-sections not need to overlap, ie each sub-section shall be closed before starting the next subsection), leaving complete freedom to the developer or the designer regarding the structure and organization later.
Tags – Tag header
The tags used in the section headers are typically of a different type from those used in the body section, being intended for different purposes. The tags used in the section headers are not normally displayed by the browser but are used as control information and services:
- Meta data to convey useful information to external applications (e.g., search engines) or browser (e.g., character encoding, useful for displaying non-Latin alphabets)
- Http-equiv meta data to control additional information in the HTTP protocol
- Links to other external services (CSS, scripts, icons displayed in the address bar of your browser)
- Insert script (executable code) used by the document
- Style information (CSS premises)
- The title associated with the page and displayed in the main browser window
Tag of the body
Within the body section, which contains the viewable part of the document, provided you use specific tags for formatting content accessible to the end user, i.e., for the control of:
- Headers (titles of chapters, paragraphs, etc.)
- Structure of text (indented text, paragraphs, etc.)
- Text appearance (bold, italics, etc.)
- Lists and lists (numbered, generic definition)
- Tables
- Electronic forms (fields that can be filled – user-selected fields, pull down menu, buttons, etc.)
- Hyperlinks and anchors
- Generic layout of the document
- Inserting images
- Inclusion of multimedia content (audio, video, animation, etc.)
- Inclusion of interactive content (scripts, external applications)
Among those listed above, the tag <a> is playing a key role because it describes a link (or links) to another hypertext document and allows, with the click of a mouse or keyboard operation, abandoning the page or site you are viewing and uploading one indicated by the link, thus realizing the navigation function typical of Internet use.
Study: From Wikipedia, the free encyclopedia. The text is available under the Creative Commons.
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Tags: HTML, HyperText Markup Language