is the !DOCTYPE? Is it mandatory to use in HTML5?

The !DOCTYPE is an instruction to the web browser about what version of HTML the page is written in. The !DOCTYPE tag does not have an end tag. It is not case sensitive.

WHAT are some other advantages of HTML5?

Cleaner markup than earlier versions of HTML
Additional semantics of new elements like header, nav, and time

is the purpose of HTML5 versus XHTML?

HTML5 is the next version of HTML 4.01, XHTML 1.0 and DOM Level 2 HTML. Its aim to reduce the need for proprietary plug-in-based rich internet application (RIA) technologies such as Adobe Flash, Microsoft Silverlight etc.

What is a Web Worker?

A web worker is a JavaScript which runs in the background.

What is a Manifest file?

A Manifest file is a simple text file that tells the browser what to cache and what not to cache.

Differentiate between session Storage and local Storage objects?

Session Storage object stores the data only for one session while local Storage object stores the data without an expiry date.