Web browsers: Understanding screen rendering and web accessibility

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A Web browser must be able at least to display the text of a web page. A text browser often displays nothing more.

However, commonly used browsers work in graphical mode and are able to use an elaborate typography, add images in the text, play music and animations and interact with the user actions.

A web page is written in a computer language: Hypertext Markup Language (HTML), which gives the browser the ability to display the text and the overall structure of the layout: title and paragraphs, lists, tables.

The layout can be refined by the use of cascading style sheets (CSS): margins, alignment, spacing, colors, borders, etc..

The position of the images in a web page is provided by HTML. Images are usually in a data format of the three following: GIF, JPEG or PNG.

Web Accessibility.

Most browsers allow you to print Web pages in black and white or color. In addition, special arrangements can be used to compensate for a visual or motor impairments.

Scripts

In the context of the Web, a script is a built-in Web page and executed by the browser computer program. A script allows simple as checking the data entered in a form tasks, manage menus or response to the movement of the mouse pointer.

The main client-side scripting language is JavaScript. This language is standardized by ECMA under the name ECMAScript.

Plugins

Browsers can easily manage all formats of existing and future data, browser vendors were asked to develop a mechanism of expansion modules that take the name of plugins, or ActiveX controls for Internet Explorer.

These can be displayed directly in the browser window data from a wide variety of formats from PDF documents to multimedia content. This mechanism also allows the use of client-side programming languages such as Flash animations, Java applets or Silverlight technology.

The wide distribution of a plugin is required for a data format has a chance to win on the Web, we often find a free download from sites software companies to create a content type particular.

Protocols

The HTTP protocol is not only a web browser can use. It also supports file transfers using FTP or WebDAV, and establish secure using HTTPS (HTTP over SSL) connections.

Some browsers (like Firefox) support the Gopher protocol shortly before HTTP became confidential and today. These communication protocols are usually standardized by the IETF.

Security vulnerabilities of web browsers

Because of high diffusion web browsers are a prime target for hackers wanting to harm users.

The user is threatened via their browser to be victim of the following attacks:

  • profilisation and behavioral analysis for marketing;
  • theft of personally identifiable information by accessing data files;
  • phishing scam;
  • crash the computer.

Either component of a web browser consists of different well-defined modules which perform separate functions and each having their own vulnerabilities:

  • an interpreter URL vulnerable to phishing attacks;
  • an interpreter HTML or XHTML (most recent) may be a misinterpretation of instructions code description;
  • a shell scripting (JavaScript, VBScript …) vulnerable to endless loops in farms bugs;
  • an application execution environment (Java Applet, ActiveX, plugins);
    a toolbar.

 

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