Web browsers communicate with Web servers primarily using HTTP (hypertext transfer protocol) to fetch webpages.
HTTP allows Web browsers to submit information to Web servers as well
as fetch Web pages from them. The most commonly used HTTP is HTTP/1.1,
which is fully defined in RFC 2616. HTTP/1.1 has its own required standards that Internet Explorer does not fully support, but most other current-generation Web browsers do.
Pages are located by means of a URL (uniform resource locator, RFC 1738 ), which is treated as an address, beginning with http: for HTTP access. Many browsers also support a variety of other URL types and their corresponding protocols, such as gopher: for Gopher (a hierarchical hyperlinking protocol), ftp: for FTP (file transfer protocol), rtsp: for RTSP (real-time streaming protocol), and https: for HTTPS (an SSL encrypted version of HTTP).
The file format for a Web page is usually HTML (hyper-text markup language) and is identified in the HTTP protocol using a MIME content type. Most browsers natively support a variety of formats in addition to HTML, such as the JPEG, PNG and GIF image formats, and can be extended to support more through the use of plugins. The combination of HTTP content type and URL protocol specification allows Web page designers to embed images, animations, video, sound, and streaming media into a Web page, or to make them accessible through the Web page.
Early Web browsers supported only a very simple version of HTML. The
rapid development of proprietary Web browsers led to the development of
non-standard dialects of HTML, leading to problems with Web
interoperability. Modern Web browsers support a combination of
standards- and defacto-based HTML and XHTML,
which should display in the same way across all browsers. No browser
fully supports HTML 4.01, XHTML 1.x or CSS 2.1 yet. Currently many
sites are designed using WYSIWYG HTML generation programs such as Adobe Dreamweaver or Microsoft FrontPage. Microsoft FrontPage often generates non-standard HTML by default, hindering the work of the W3C in developing standards, specifically with XHTML and CSS (cascading style sheets, used for page layout). Dreamweaver and other more modern Microsoft HTML development tools such as Microsoft Expression Web and Microsoft Visual Studio conform to the W3C standards.
Some of the more popular browsers include additional components to support Usenet news, IRC (Internet relay chat), and e-mail. Protocols supported may include NNTP (network news transfer protocol), SMTP (simple mail transfer protocol), IMAP (Internet message access protocol), and POP (post office protocol). These browsers are often referred to as Internet suites or application suites rather than merely Web browsers.
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