I read this conversation: http://stackoverflow.com/questions/11436219/html5-app-with-appcelerator-titanium and I am becoming confused!
Titanium Mobile Web is a ground-up port of the Titanium API to the mobile web. We use several browser technologies, some of which are categorized as "HTML5". For example, Titanium Mobile Web uses the HTML5 <video> tag for the Ti.Media.VideoPlayer.
There are several APIs that Titanium Mobile Web uses that are NOT HTML5 such as Geolocation API and a ton of CSS3 features like transforms, gradients, etc.
The native iOS and Android platforms do not have anything to do with HTML5, however, you can certainly create a native iOS or Android app with a WebView and stuff HTML5 stuff in it.
It's worth clarifying that Titanium Mobile Web apps require a web server and are not distributed through the Apple App Store or the Android Playstore.
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