The following tables compare HTML 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. Version number, if possible, is provided for feature that is fully supported (based on HTML 4.01). Proprietary extensions are not included.