XPath, implemented in TransforMiiX Gecko also supports SVG. Legacy IE non-standard support In order to support web pages designed for legacy versions of Netscape and Internet Explorer, Gecko supports DOCTYPE switching. Documents with a modern DOCTYPE are rendered in standards compliance mode, which follows the W3C standards strictly. Documents that have no DOCTYPE or an older DOCTYPE are rendered in quirks mode, which emulates some of the non-standard oddities of Netscape Communicator 4.x; however, some of the 4.x features (such as layers) are not supported. Gecko also has limited support for some non-standard Internet Explorer features, such as the marquee element and the document.all property (though pages explicitly testing for document.all will be told it is not supported). Usage Gecko is primarily used in web browsers, the earliest being Netscape 6 and Mozilla Suite (later renamed SeaMonkey). It is also used in other Mozilla web browser derivatives such as Firefox and Firefox for mobile and the implementation of the Internet Explorer-clone that is part of Wine. Mozilla also uses it in their Thunderbird email-client. Other web browsers using Gecko include GNU IceCat, Waterfox, K-Meleon, Lunascape, Portable Firefox, Conkeror, Classilla, TenFourFox. Gecko is also used by Sugar for the OLPC XO-1 computer. Gecko is used as a complete implementation of the XUL (XML User Interface Language). Gecko currently defines the XUL specification. Past users Products that formerly used Gecko include Pale Moon (now using Goanna), Epiphany (now known as GNOME Web and using WebKitGTK), and GNOME DevHelp (now using WebKitGTK.) Discontinued products that used Gecko include Swiftfox, Flock, Galeon, Camino, Minimo, Beonex Communicator, Kazehakase, Songbird, Sunbird (calendar), MicroB, Nightingale, Instantbird, and Picasa for Linux. Proprietary dependency On Windows and other platforms, Gecko depends on proprietary compilers. Thus, FOSS distributions of Linux cannot include the Gecko package used in the Windows compatibility layer Wine. After Gecko 2.0, the version number was bumped to 5.0 to match Firefox 5, and from then on has been kept in sync with the major version number for both Firefox and Thunderbird, to reflect the fact that it is no longer a separate component. Bloat In the Netscape era, a combination of poor technical and management decisions resulted in Gecko software bloat. Thus in 2001 Apple chose to fork KHTML, not Gecko, to create the WebKit engine for its Safari browser. However, by 2008 Mozilla had addressed some of the bloat problems, resulting in big performance improvements