Standards support

Internet Explorer, using the Trident layout engine, almost fully supports HTML 4.01, CSS Level 1, XML 1.0 and DOM Level 1, with minor implementation gaps. It partially supports CSS Level 2 and DOM Level 2, with some implementation gaps and conformance issues. XML support brings with it support for XHTML, however Microsoft has buried this support since IE 5.0 making it difficult to access. Like other browsers it can consume XHTML when served as MIME type “text/html”. It can also consume XHTML as XML when served as MIME types “application/xml” and “text/xml”, however this requires a small XSLT measure to re-enable the XHTML as XML support. It pretends to not comprehend XHTML when vended in the preferred type as “application/xhtml+xml” and instead treats it as an unfamiliar file type for download.

Internet Explorer uses DOCTYPE sniffing to choose between "quirks mode" (renders similarly to older versions of MSIE) and standards mode (renders closer to W3C's specifications) for HTML and CSS rendering on screen (for printing Internet Explorer always uses standards mode). It fully supports XSLT 1.0 or the December 1998 Working Draft of XSL, depending on the version of MSXML (a dynamic link library) available. It also provides its own dialect of ECMAScript called JScript.