Editing Gecko (software) (section)

==Legacy IE non-standard support==
{{main|Quirks mode}}
In order to support [[web page]]s designed for legacy versions of Netscape and Internet Explorer, Gecko supports [[document type declaration|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 [[Layer (HTML tag)|layers]]) are not supported.

Gecko also has limited support for some non-standard Internet Explorer features, such as the [[marquee element]] and the <code>document.all</code> property (though pages explicitly testing for <code>document.all</code> will be told it is not supported).<ref>{{cite web |url = http://www.mozillazine.org/talkback.html?article=5063 |title = Mozilla Adds Undetectable document.all Support, Part of New Novell Linux Distribution?|publisher = Developer.mozilla.org |date = 2004-07-23 |access-date = 2018-02-07}}</ref>