Dean mentioned a bunch of things we are doing in Internet Explorer 8 Beta 1 for Developers. I want to point you to more details specifically about the developer focused changes to CSS, the DOM and the new version targeting.
Standards support (CSS/HTML)
IE8 improves rendering of content authored to various web standards in standards mode. As we have mentioned before, IE8 Beta 1 for Developers ships with standards mode as its default formatting engine. In order to maintain backwards compatibility, sites can opt-into IE7-like handling of content by inserting a special meta element into the web page, that triggers the "IE7 standards mode". For more complete details regarding document compatibility, see Defining Document Compatibility.
While the behavior of the browser is unchanged from Internet Explorer 7 in "IE7 Standards Mode", in standards mode (the default IE8 rendering mode), IE8 supports Data: URIs, the abbr tag, CSS generated content, the display: table CSS properties, in addition to fixing a lot of CSS and HTML parsing bugs. For a complete list, see CSS Improvements in Internet Explorer 8.
Standards support (DOM) and AJAX
CSS is not the only place where we tuned IE8, we tweaked the DOM as well. IE8 features an enhanced and standardized DOM that brings it in line with implementations in other browsers. Highlights include changes in the behavior of the getAttribute, setAttribute and removeAttribute modifiers to make IE8 more interoperable with other browsers. Additionally, IE8 has dramatically enhanced AJAX support with features like DOM: Storage, Cross Document Messaging (XDM) and the Selectors APIs. For a more complete list of AJAX and DOM improvements, see What’s New in Internet Explorer 8.
Last but certainly not least, we have added support for the Accessible Rich Internet Applications (ARIA) specification. This specification describes how site authors can mark up their content semantically such that users who might use assistive technologies may more completely experience the content. See What’s New for Accessibility in Internet Explorer 8 for a comprehensive discussion of this topic.
It has been great to see all of the wonderful feedback on the beta thus far and remember that IE8 is still a work in progress. Stay tuned for more details here on our blog and on the IE Development Center on MSDN.
Thanks and Happy Browsing,
Principal Program Management Lead
Internet Explorer Developer Experience Team