212 Chapter 8—Web Storage and Offline Web Applications
Figure 8.3 Opera displaying Developer ToolsEven Internet Explorer 9 offers Developer Tools. Apart from the DOM tree, CSS
properties, a script debugger, and network profiling, there is a browser console
that works in a similar way to that in Firebug, Safari, Chrome, and Opera.The latest browser versions really excel regarding the functions of their developer
tools. Not only can cookies, sessionStorage, and localStorage be scrutinized, but
these tools are also a big help in many other areas of web development.8.2 Offline Web Applications
To make applications run completely without network access, HTML, Java-
Script, and multimedia files must be reliably saved on the client machine. Up un-
til now, all browsers had certain functions for caching content, but there was no
standardized access to this content. The HTML5 specification took this problem
to heart and devoted a section to Offline Web applications. They agreed on an in-
dependent offline memory, controllable with a simple configuration. A file with
the ending .appcache contains the elements to be saved in the offline memory. It
is integrated in the html tag as a manifest attribute:<!DOCTYPE html>
<html manifest="menu.appcache">
<head>