Report Html Or Xhtml? [Updated: 14 Sept. 2011] in HTML/XHTML Posted June 12, 2013 · Edited June 12, 2013 by Wickham ...but lots of people are using HTML5 as it gives some extra benefits. When you use a validator you just get a warning Using experimental feature: HTML5 Conformance Checker. The validator checked your document with an experimental feature: HTML5 Conformance Checker. This feature has been made available for your convenience, but be aware that it may be unreliable, or not perfectly up to date with the latest development of some cutting-edge technologies. If you find any issues with this feature, please report them. Thank you. Personally, I am using HTML5 but I don't use all the new features and I check on several browsers and hand-held devices using Opera Mobile Emulator http://www.opera.com/developer/mobile-emulator which gives lots of mobile devices to check.