Described a semi-new method for “enabling” unknown elements in IE8 – the...

... namespaced “end element” method

For completeness, added description of a JavaScript free way (that is: markup based) way of “enabling” support for unknown/custom elements in IE8 (including IE8,IE9,IE10 and IE11 in compatibility mode).

The method is basd on an unknown, namespaced “end element” — </x xmlns="x"/>, which goes right after the DOCTYPE, and which disappaers from the DOM (in legacy IE as well as in conforming HTML5 parsers), but which has as effect that all unknown elements (except elements with a colon:prefix) are handled “properly” by IE (that is: it makes IE recognize them as elements, just like the document.createElement('foo'); method does), except that it (unlike the createElement method) doesn’t “update” the CSS selector engine, with the consequence that the author must instead use attribute based selectors.