It was first introduced with the release of Internet Explorer version 4.0 in October 1997; it has been steadily upgraded and remains in use today. For versions 7 and 8 of Internet Explorer, Microsoft made significant changes to the Trident layout engine to improve compliance with web standards and add support for new technologies. Since then, Microsoft intends to comply with many modern web standards, and also intends to significantly update the layout engine to be more competitive and modern compared to other current layout engines.
Trident was designed as a software component to allow software developers to easily add web browsing functionality to their own applications. It presents a COM interface for accessing and editing web pages in any COM-supported environment, like C++ and .NET. For instance, a web browser control can be added to a C++ program and Trident can then be used to access the page currently displayed in the web browser and retrieve element values. Events from the web browser control can also be captured. Trident functionality becomes available by linking the file mshtml.dll to the software project.
Netscape Browser (Netscape 8), which used Trident to render web pages in IE mode
Pyjamas, a python Widget set Toolkit. Embedding IWebBrowser2 as an Active-X component and accessing the COM interface, Pyjamas uses Trident for the Desktop version, through the python win32 "comtypes" library.
Valve's Steam client, previous versions of which used Trident to render the "Store", "Update News" and "Community" sections as well as the Steam in-game browser and MOTD screens in Valve games. The Steam client was updated to use WebKit instead of Trident for these features.
Current versions of Trident, as of Internet Explorer 9 have introduced support for CSS 3, HTML5, and SVG, as well as other modern web standards. Web standards compliance was gradually improved with the evolution of Trident. Although each version of IE has improved standards support, including the introduction of a "standards-compliant mode" in version 6, the core standards that are used to build web pages (HTML and CSS) were sometimes implemented in an incomplete fashion. For example, there was no support for the <abbr> element which is part of the HTML 4.01 standard prior to IE 8. There were also some CSS attributes missing from Trident, like min-height, etc. as of IE 6. As of Internet Explorer 8 CSS 2.1 is fully supported as well as some CSS 3.0 attributes. This lack of standards compliance has been known to cause rendering bugs and lack of support for modern web technologies, which often increases development time for web pages. Still rendering differences of HTML between standards-compliant browsers are not completely resolved yet.
Apart from Trident, Microsoft also has and uses several other layout engines. One of them, known as Tasman, was used in Internet Explorer 5 for Mac. Development of Internet Explorer for Mac was halted in roughly 2003, but development of Tasman continued to a limited extent, and was later included in Office 2004 for Mac. Office for Mac 2011 uses the open source WebKit engine. Microsoft's now defunct web design product, Expression Web as well as Visual Studio 2008 and later do not use Internet Explorer's Trident engine, but rather a different engine.
In 2014, Trident was forked to create the engine EdgeHTML for Microsoft Edge on Windows 10. The new engine is "designed for interoperability with the modern web" and deprecates or removes a number of legacy components and behaviors, including document modes, ensuring that pure, standards-compliant HTML will render properly in browsers without the need for special considerations by web developers. This resulted in a completely new browser called Microsoft Edge, which replaces Internet Explorer as a stock browser of Windows and a base of Microsoft's web related services.
^Mauceri, Rob (April 16, 2007). "Office Live and SharePoint". Microsoft SharePoint Designer Team Blog. Microsoft. Retrieved August 23, 2010. SharePoint Designer doesn't use Trident. SharePoint Designer, Expression Web, and the next version of Visual Studio's Visual Web Designer (code name Orcas) all use the same standards-based web design component. This component was developed jointly by the three product teams for high fidelity rendering of web standards like CSS, XHTML, as well as ASP.net.