Comparison of layout engines (Non-standard HTML)

The following tables compare deprecated and proprietary HTML elements and attributes compatibility and support for a number of layout engines. Please see the individual products' articles for further information. This article is not all-inclusive or necessarily up-to-date. Unless otherwise specified in footnotes, comparisons are based on the stable versions without any add-ons, extensions or external programs.

In the early years of the World Wide Web, the standards which today are used in most web browsers and web pages were mostly non-existent. Different browsers and HTML editors were being offered by competing vendors such as Netscape, Microsoft and WebTV, all of whom possessed their own ideas for how web sites should be constructed. These varying standards resulted in web developers coding for specific web browsers, using elements which could often be recognized by only one browser.