Trident (also known as MSHTML) is the name of the layout engine for the Microsoft Windows version of Internet Explorer. It was first introduced with the release of Internet Explorer version 4 in October 1997, has been steadily upgraded and remains in use today. For version 7 of Internet Explorer, Microsoft made significant changes to the Trident layout engine to improve compliance with web standards and add support for new technologies. Despite these changes, Trident remains significantly less compliant than competing layout engines Gecko, Presto and WebCore.
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 connecting the file mshtml.dll to the software project.
Alternatively, Microsoft also has several other layout engines. One of them, known as Tasman, was used in Internet Explorer for Mac. Tasman is known for its better standards support. Contrary to popular belief, although development of Internet Explorer for Mac has halted, development of Tasman continues, with its most recent release as part of Office 2004 for Mac. Microsoft's new web design product, Expression Web does not use Internet Explorer's Trident engine, but rather its own engine which Microsoft claims is the most standards-compliant on the market today.