Features of Internet Explorer
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Internet Explorer has been designed to view the broadest range of web pages without major problems. During the heydays of the historic browser wars, Internet Explorer embraced Netscape by supporting many of the progressive features of the time. For a long period after the introduction of version six, there was no further development on the browser. Major development on the browser restarted in 2004 for Windows XP SP2 and continues in IE7.
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[edit] Component architecture
Trident, the layout engine used by Internet Explorer, is a separate library. It is therefore able to be implemented by other programs, including the operating system. It also utilizes the Component Object Model technology, allowing it to incorporate new features dynamically. This task is accomplished using one of two interfaces, namely ActiveX or Browser Helper Objects.
ActiveX, which was introduced with Internet Explorer 3.0, allows web pages to extend their functionality by providing access to native operating system calls. This has been the source of security concerns, as this access was originally unrestricted and unchecked.
Browser Helper Objects, which were introduced with Internet Explorer 4.0, enable the addition of features to the browser itself. They are provided through dynamically-linked libraries, more commonly known as DLLs. It also provides the functionality for web pages to provide and install helper objects. Because these objects are linked into the executable code of the browser, they also create security concerns. Internet Explorer 6.0, Service Pack 2 provides an Add-on Manager for controlling Browser Helper Objects.
[edit] Usability and accessibility
Comparatively speaking, the default Internet Explorer interface is less cluttered than some of the Internet suites such as Netscape Communicator, Mozilla Application Suite, and Opera. With IE7, the interface has become even more streamlined, redesigning the interface to the most minimal possible. The interface can be modified should the user prefer it that way.
Since it is tightly integrated with the operating system, Internet Explorer makes full use of the accessibility framework provided in Windows. Internet Explorer is also a user interface for FTP, with operations similar to that of Windows Explorer. However, with version 7.0, FTP sites are rendered in a hyperlinked page, with the folder-like view available if the site is accessed from Windows Explorer. IE7 can itself lauch Windows Explorer for FTP sites.
The ability to block pop-up windows (unrequested windows created with JavaScript) was introduced with Internet Explorer 6.0, Service Pack 2. However, to limit other scripting functions, such as those that modify the status bar or adjust the size and position of the browser window, IE7 is needed.
Tabbed browsing functionality was introduced with IE7, augmented with an ability to view these quickly with "Quick Tabs", an RSS-rendering capabilities, feed discovery, and intelligent print layouts, with the shrink-to-fit feature resizing page layout to fit in the paper margins. Tabbed browsing can be added to previous versions using add-ons, like MSN Toolbar, which added tabbed browsing functionality, though much less refined than the native implementation in IE7, to IE6.
[edit] Security framework
Internet Explorer uses a zone-based security framework, which means that sites are grouped based upon certain conditions. IE allows the restriction of broad areas of functionality, and also allows specific functions to be restricted. The administration of Internet Explorer is accomplished through the Internet Properties control panel. This utility also administers the Internet Explorer framework as it is implemented by other applications.
Patches and updates to the browser are released periodically and made available through Windows Update web site. Microsoft's recent Windows XP Service Pack 2 adds several important security features to Internet Explorer, including a popup blocker and additional security for ActiveX controls. ActiveX support remains in Internet Explorer although access to the "Local Machine Zone" is denied by default since Service Pack 2. However, once an ActiveX control runs and is authorized by the user, it can gain all the privileges of the user, instead of being granted limited privileges as Java or JavaScript do. The Windows Vista version of IE 7 will support running the browser in a low-permission mode, making malware unable to run unless expressly granted permission by the user.
As of May 2005, Secunia has reported 19 unpatched vulnerabilities in Internet Explorer. All of the vulnerabilities are still unpatched for Internet Explorer on earlier versions of Windows, since many of the vulnerabilities were patched in Service Pack 2 only.
Although security patches continue to be released for a range of platforms, most recent feature additions and security improvements were released for Windows XP only.
[edit] Standards support
Internet Explorer offers support for HTML 4.01, CSS Level 1, XML and DOM Level 1, with some implementation gaps. It also offers limited or broken support for CSS Level 2, XHTML, DOM Level 2, and XSL. Internet Explorer provides its own dialect of ECMAScript called JScript.
Internet Explorer supports a variety of graphics file formats, including GIF, JPEG and partial support of PNG. Version 7.0 introduced enhanced PNG support, including alpha channels but ignores gamma information. It also includes an extended support for CSS Level 2.
[edit] Proprietary extensions
Internet Explorer has introduced an array of proprietary extensions to many of the standards, including HTML, CSS and the DOM. This has resulted in a number of web pages that can only be viewed properly using Internet Explorer. Some view this as an example of what is called "embrace, extend and extinguish" (EEE), a way to drive competitors out of business by forcing them to use proprietary technology that Microsoft controls, resulting in vendor lock-in.
Internet Explorer has introduced a number of extensions to JScript which have been adopted by other browsers. These include the innerHTML property, which returns the HTML string within an element; the XMLHttpRequest object, which allows the sending of HTTP request and receiving of HTTP response; and the designMode attribute of the contentDocument object, which enables rich text editing of HTML documents. Some of these functionalities were not possible until the introduction of the W3C DOM methods. Its Ruby character extension to HTML is also accepted as a module in W3C XHTML 1.1, though it is not found in all versions of W3C HTML.
The favicon (short for "favorites icon") introduced by Internet Explorer is now also supported and extended in other browsers. It allows web pages to specify a 16-by-16 pixel image for use in bookmarks. Originally, support was provided only for the native Windows ICO format, however it has now been extended to any type of images such as PNG and GIF.
When Internet Explorer was being actively developed, Microsoft sent several proposals of Web standards to W3C. However, all were rejected, at least in their original forms. These include the 'behavior' CSS property, which connects the HTML elements with JScript behaviors (known as HTML Components, HTC); HTML+TIME profile, which adds timing and media synchronization support to HTML documents (similar to the W3C XHTML+SMIL); and the VML vector graphics file format. VML was, however, subsequently combined with PGML (proposed by Adobe and Sun), resulting in the W3C-approved SVG format, currently one of the only vector image formats being used on the web.
Other proprietary standards include:
- Support for vertical text, but in a syntax different from W3C CSS3 candidate recommendation.
- Support for a variety of image effects and page transitions, which are not found in W3C CSS.
- Support for obfuscated script code, in particular JScript.Encode .
